This has led to the club being investigated or charged by both the SPFL and UEFA for infringements of their rules regarding fan behaviour.
I'm not concerned here with the Offensive Behaviour Act (which is a nonsensical piece of legislation and should be repealed ASAP), but with the content of the banners themselves.
The Green Brigade were making a valid point about the similarities (although let's not take that too far because there are significant differences too) between the Republican armed struggle of the 1970's - 1990's and the 13th - 14th Century struggle for Scottish independence. They also have a point that the Offensive Behaviour Act is an unacceptable attack on freedom of expression. That though is not my concern here either.
It may well be a freedom of speech/expression issue, but having a right to do something doesn't mean you have to, or even should, do it.
At heart this issue is about an insistence on showing support for the Irish Republican cause at Celtic matches. I've no problem with anyone being a Republican, although it's not an ideology I share myself. I've no problem with anyone displaying their support for Republicanism either, but in an appropriate setting, which I do not believe a Celtic match is.
So here is the heart of the argument - how far is Republicanism a part of Celtic's DNA?
I'll define my terms before going on. "Celtic," is Celtic FC, founded 1887, incorporated as a limited liability company in 1897 and floated on the stock market as Celtic plc in 1994.
"Republicanism" is the political ideology espoused by Provisional Sinn Fein, tracing its roots to Wolfe Tone's Republicanism of 1798 by way of the First Dail 1919.
On what basis is Celtic claimed to have been Republican, or associated with Republicanism right from the start?
It usually revolves around the patronage of the club by Michael Davitt, who laid a sod of Donegal turf in the centre circle of the original Celtic Park.
Does this mean the club endorsed Republicanism? For me that is quite a stretch.
Michael Davitt was certainly a Republican at one stage in his life. He was a member of the Irish Republican Brotherhood and was sentenced to 15 years' imprisonment in 1870 for his part in arms smuggling. He was released after serving half of his sentence in 1877 and rejoined the IRB, becoming a member of its Supreme Council.
While imprisoned, Davitt came to believe that the only way the people's lives could be improved was by being given ownership of their land. He devoted the next part of his political career to enabling tenant farmers to buy their land from absentee landlords.
From 1878 - 1881 the Irish National Land League, with the support of Charles Stewart Parnell, campaigned for tenants' rights, specifically "the Three F's," (fair rents, fixity of tenure, and free sale). Their strategy was one of withholding of rents, resisting evictions, and eventually ostracism of the worst of the landlords, the first target being Captain Charles Boycott.
The Land Act of 1881 secured Davitt's objectives.
When Celtic was founded in 1887, what exactly was it that made Davitt a hero to so many? Was it his IRB gun smuggling activities, or his heroic efforts on behalf of Irish tenant farmers which, with it's renunciation of violence, inspired Mahatma Gandhi some 70 years later?
Of course we may never know definitively the answer to that question, but what is the likelihood? Republicanism was a fringe movement in Ireland at the time and the vast majority of the people were supporters of Parnell and Home Rule.
It is debatable by this point whether Davitt can even be accurately described as a Republican. Throughout the 1890's he was a Member of Parliament for the Irish Parliamentary Party and when he died in 1906 his funeral was attended by The Lord Lieutenant of Ireland.
That Davitt was at one time a Republican is indisputable. That he was Republican in 1888 is less clear.
Given the popularity of Parnell and the Irish Party of which Davitt was an ally, and his fame for helping the downtrodden tenant farmer, it is far from clear that the newly formed Celtic approached him on account of his Republicanism. His later career in the House of Commons suggests he would hardly have been the sort to lie in wait for Mick Collins at Béal na Bláth.
Barring solid evidence to the contrary, it is impossible to say with certainty what the political leanings of the founders of Celtic were. On the balance of probability, I consider it highly unlikely that all, or even many of them, were Republicans.
Of course, even if they were, that by itself would not make Republicanism intrinsic to Celtic. What did Celtic say about itself?
The first circular, issued by the club in January 1888, said this:
CircularCELTIC FOOTBALL AND ATHLETIC CLUB
CELTIC PARK, PARKHEAD
(Corner of Dalmarnock and Janefield Streets)
His Grace the Archbishop of Glasgow and the Clergy of St. Mary's, Sacred Heart and St. Michael's Missions, and the principle Catholic laymen of the East End
The above club was formed in November 1887 by a number of the Catholics of the East End of the City.
The main objective of the club is to supply the East End conferences of the St. Vincent De Paul Society with funds for the maintenence of the "Dinner Tables" of our needy children in the Missions of St Mary's, Sacred Heart, and St. Michael's. Many cases of sheer poverty are left unaided through lack of means. It is therefore with this principle object that we have set afloat the "Celtic", and we invite you as one of our ever-ready friends to assist in putting our new Park in proper working order for the coming football season.
We have already several of the leading Catholic football players of the West of Scotland on our membership list. They have most thoughtfully offered to assist in the good work.
We are fully aware that the "elite" of football players belong to this City and suburbs, and we know that from there we can select a team which will be able to do credit to the Catholics of the West of Scotland as the Hibernians have been doing in the East.
Again, there is also the desire to have a large recreation ground where our Catholic young men will be able to enjoy the various sports which will build them up physically, and we feel sure we will have many supporters with us in this laudable object.
Not a trace of Republicanism, nor even Nationalism to be found there. It is clear that the driving impulse behind the foundation of Celtic in 1887 was Catholic charity. Celtic was, and remained for long, a Catholic club far more than a Republican one.
Of course many Celtic fans have, at least since 1916, been ardent Republicans, but that does not make the club so.
The question remains though - should Celtic supporters sing Republican songs at Celtic matches?
In my opinion, you should have a right to do so, but that does not mean you should.
I find the argument that Celtic has Republican roots to be very weak. No one can say the founders of the club were Republican - the liklihood is that they were not. It is also a stretch to say that by approaching Michael Davitt that the club endorsed his Republicanism.
What I feel the rebel singers should be doing is considering the feelings of other people. No one in their right minds would visit Dresden and sing songs glorifying the brave men who firebombed the city in 1945.
By the same token, a great many decent people, without a bigoted thought in their heads, find songs glorifying the organisation that bombed Warrington decidedly distasteful.
Whether we like it or not, we share this country with people who will never, ever accept the Provisional IRA as romantic freedom fighters. That many songs refer to a different incarnation of the IRA is a fine distinction that most people are unwilling to consider. And furthermore, most of these people have no axe to grind with Ireland or the Irish.
William Wallace may have done some violent things, but he has been dead these past 700 years. There's no one alive today whose son, daughter, husband, wife, parent or grandparent were killed in the Scottish wars of independence. The wounds from the Troubles are still too raw for too many people to appreciate having to listen to people at football matches singing songs in support of either side in the conflict.
You can argue all you like that people need to be educated about what went on in Ireland in the 20th Century and before, but who wants to listen to a load of football fans singing about it on their tv's when all they want to do is enjoy a match?
I often hear people say they have no problem with Catholics, but they do have a problem with Catholicism. For me, when it comes to Irish Republicanism, it's the other way round.
I draw an important distinction here between the people who are active in Republican politics in Ireland, and the Scottish singers of the songs at Celtic matches. I find nothing morally objectionable about Republicanism, and people are fully entitled to pursue its ends legitimately.
What I have a problem with is Scottish Celtic supporters using the club as a platform to spout their support for a cause which, let's be honest, most of them know little about, while telling us that they are the real Celtic supporters for doing so. That singing about Bobby Sands rather than Bobby Murdoch means they are following in the footsteps of the Marist Brother who founded the club more closely than those of us who object to their choice of songbook.
This would be an academic debate if only the songs and banners didn't hurt the club they profess to love.
We've been fined repeatedly by UEFA over the past few years, including for "illicit" banners and chants supporting Irish Republicanism. If this doesn't stop, we could be facing away bans (as happened to old Rangers for sectarian chanting before they shuffled off their mortal coil) or stand closures.
So please, campaign against the Offensive Behaviour Act all you like. Outside Holyrood would be a good place to start.
Be as Republican as you like, I'm sure Sinn Fein would welcome your feet on the ground knocking doors all over Ireland at election time. Not sure your singing at Celtic Park does the cause much good though.
But please don't tell me that by singing Republican songs you are fighting for my right of free speech, or being true to the roots of the club we both love.
One final note - I've lost count of the number of times over the past week I've seen or heard someone say the club wants to lose its Irish roots and become a Glasgow version of Hibs.
That's nonsense. Celtic is a Scottish club with proud Irish roots and that will never, ever be forgotten, especially by people like me who are equally proud of their own Irish roots. But Republicanism is a political ideology, not a nationality and you don't have to be Republican to be Irish. Nor is it the only authentic expression of Irishness.
Let the people sing their stories and their songs, but we might all like different songs and you might not like all of them. Far better to sing about what unites us as Celtic fans rather than divides us.