Indeed, one of its founding players, later chairman - my grandfather, James Kelly - lost two sons to the First World War. Celtic was proud to parade former player William Angus, who won the Victoria Cross in the same futile conflict. And Desmond White, another chairman, was wounded flying for the RAF in the Second World War. No Celtic players were transferred into reserved occupations like ship-building to avoid the draft.
So the club was right to distance itself from the views of Saturday's protesters. Whether it now should go on to punish those involved - if it manages to identify them - is another matter. I personally would defend the right of any group of fans to express its political views. Not to the death, as Voltaire might have (that's a bit too extreme), but to the extent of not trying to invoke sanctions against them.
Freedom of speech is one of the fundamental rights we are proud to defend. David Cameron did just that yesterday in China. Why should this right be restricted when one enters a football stadium? Especially to support Celtic, whose long tradition has been to fight discrimination and to defend the rights of minorities. Celtic has never, as a club, been afraid to speak out in favour of the oppressed. The club gained respect throughout Europe when Sir Robert Kelly as chairman succeeded in getting the Soviet Union kicked out of European competition after its violent suppression of the Czechoslovakian revolution in the spring of 1968. Incidentally, when Sir Robert was granted his knighthood he was greeted with jubilant applause at the next home game. No condemnation of the British monarchy or its powers of patronage that day.
Among supporters, too, there has always been identification with the underdogs of international politics. Palestinian flags are displayed - not Israeli ones. The Basque separatist cause finds sympathy. Equally and paradoxically, John F Kennedy, that belligerent US president who brought us to the brink of nuclear war, was a folk hero to the Jungle.
All of this awareness of and interest in politics is part of the history of Celtic that makes it more than just a football club. Its origins are unique, founded not so men could have fun playing football, not as a commercial venture, but to raise money for the children of the Catholic poor in the East End of Glasgow. That has given the club and its supporters a dimension of social awareness and responsibility that no other Scottish club has.And from the start Celtic was a Scottish, not Irish, club. Founded by the sons of Irish immigrants it rejected the name Glasgow Hibernian in favour of Celtic because it wanted to integrate this new community with its host society.
But the current guardians of the club's traditions seem to be falling between over-sensitivity in an age of political correctness and the pursuit of financial success. A club founded to alleviate the poor from its misery should not be promoting alcohol on its jerseys. That is surely much more offensive to the memory of Brother Walfrid - whose role in the founding of the club has been greatly exaggerated in recent years - than poppies. And as for having a bookies' shop touting for business within the stadium, that displays an indifference to another great social evil that bedevils the poor.
On the other hand, the club announces an apology for the Saturday's banner. For what? The club didn't display it or condone its message. It had no need to say sorry. But that is the cult of today: to apologise for things over which we have no control. Tony Blair apologised for the Irish potato famine and the Australians are about to apologise for the white settlers' treatment of the Aboriginals.
Nor should the club apologise for the offensive chants in support of the IRA. They are sung by people who have been left behind by history. Since 9/11, terrorism is no longer a viable option for those seeking political change in the West. It is seen for the indiscriminate and vicious horror that it always was. John Reid, the current chairman, can be proud that he was an integral part of the peace process that halted the violence in Northern Ireland.
Of course his appointment as chairman was another source of controversy among supporters, because some of the rest of his political actions contradicted the traditional Celtic values. He decided to send Gary McKinnon to the US to face charges of hacking. And he severely restricted the rights of suspected Muslim terrorists enforcing detention without trial. Most people would be on Reid's side on this latter. But is it compatible with being chairman of such a club as Celtic when internment in Northern Ireland was such a divisive issue? It was legitimate for supporters to force the question.
This is difficult area, for the club is one which proudly goes with the territory. Celtic is expected to take a stand on political issues. The banners on Saturday condemned, among other things, the British involvement in Iraq. John Reid supported that invasion. But millions refused to see the operation carried out in their name. Are they condemning the Green Brigade for opposing the very same thing?
Advocate freedom of speech and you are going to have to listen to some pretty objectionable opinions. But restrict it and you diminish democracy. Sports administrators do not want politics and sport to mix. It causes too much hassle.But the international sports boycott of South Africa was one of the most effective weapons against apartheid. Celtic will get this right if it sticks to its official condemnation and leave it at that. To ban fans for expressing political views is totalitarian, and is likely to run foul of the European Convention of Human Rights.