There's a contemporary adage about political debates that whoever first brings up a Nazi comparison in an argument, loses the argument. Nothing compares to the Nazi crimes and anyone who tries to inflate their talking-point by doing so seems absurd and insensitive.
Sinn Féin's Martin Kenny (no kin) is evidently not a subscriber to this thesis, as he introduced the Nazi parallel last week in Dáil Éireann in the context of the distressful situation around the Tuam mother and baby home. The Sligo-Leitrim TD said he had "often wondered about Hitler, the Germans and what happened to the Jews and how he was able to do what he did. If you sit and think about the kind of Ireland we had, it is very easy to understand how people were able to do these things."
If Mr Kenny really did "wonder" about Hitler, the Nazis and the Third Reich, he could have done so by dipping into the archives of his own party, Sinn Féin, which, historically, is replete with examples of his historical predecessors who behaved as though they were much in sympathy with Hitler's Reich.
He might have discussed this with his colleague Mary Lou McDonald, the keynote speaker in a 2003 tribute to IRA-Sinn Féin chief of staff Sean Russell, who died in 1940 in the middle of an operation aimed at fomenting a pro-Nazi rising in Ireland. Russell forged links with the Nazis in 1938, visiting Berlin on several occasions, with a view to enlisting the Reich in the IRA's bombing campaign against England. The Reich had its own bombing plans via the Luftwaffe, but they weren't averse to the IRA's more amateur efforts with home-made terrorist attacks.
Mr Kenny could further inform himself by reading David O'Donoghue's meticulous biography of Jim O'Donovan, 'The Devil's Deal', which documents in faultless detail the links between the IRA and Nazi Germany in the 1930s and 40s. Jim O'Donovan, who died in 1979, was an ESB employee, explosives expert and chief liaison officer between the IRA and the Third Reich. He masterminded the bombing of Coventry in August 1939, just before the war against Hitler's Germany broke out. Instead of using a vehicle, as present jihadist bombers favour, O'Donovan used a bicycle bomb which killed five people and injured more than 70, in a bid to create a United Ireland - under the Nazi jackboot.
One of O'Donovan's IRA liaison officers in the English midlands was Dominic Adams, Gerry's uncle.
There are other similar characters worthy of research.
There is the enigmatic and genuinely tragic figure of the Frank Ryan, sometime editor of the Sinn Féin newspaper 'An Phoblacht', who fought on the Republican side in the Spanish Civil war - Christy Moore wrote a song in tribute to his brigade - and after being captured and languishing in a Spanish prison, was mysteriously handed over to Nazi Germany by General Franco. There, Frank Ryan resided in a Berlin flat where he found companionship and support in the sometime company of the late Helmut Clissmann and the late Francis Stuart, who would broadcast for the Reich on a special wavelength aimed at Ireland (documented in another of David O'Donoghue's books, 'Hitler's Irish Voices'.)
That Berlin flat must have been fascinating at times, while plans were afoot to despatch Ryan, the IRA-Abwehr liaison agent, in a U-boat to Ireland, so as to rescue the Irish people from British oppression, or any threat of British invasion. But Ryan died in 1944 before he could embark on his mission - either from TB, or from the effects of prison in Spain.
Another visitor to Berlin during the 1930s was Sean MacBride, sometime chief of staff of the IRA. Like Martin McGuinness after him, MacBride ultimately became an advocate of world peace, but as a young man he had adhered to the well-tried doctrine that "England's difficulty is Ireland's opportunity", and anyone who was giving the Brits a headache might be used for Ireland's national cause.
As a strategic point of view, perhaps many Irish nationalists might have justified that idea. Mao Tse Tung declared "My enemy's enemy is my friend". Russell, O'Donovan and Ryan were, it might be said, just following that strategy through.
But on the substance of hostility to the Jews, Mr Kenny (right) need only take a short walk from Dáil Éireann to the Irish Jewish Museum, at 3 Walworth Road, off Dublin's South Circular Road, where he may peruse Sinn Féin pamphlets from the 1930s on display. Anti-Semitic attitudes are openly expressed in Sinn Féin publications proudly boasting of work-places where "no Jews are employed" and exhorting Irish business to "employ Irish labour only - no Jews". Jews are portrayed as exploiters of Irish workers, money-lenders and particularly nefarious in the tailoring trade.
So go on, Martin: if you "wonder" about history, take a walk over to the Walworth Road and do the research.
I imagine that most Irish people are distressed, and indeed ashamed, of what occurred at the mother and baby homes run by the religious orders, and it behoves us to ask if our own family's attitudes made any contribution to the cruel conditions.
But there is no evidence that anyone planned to murder mothers and babies, or, indeed, a whole race of people (not forgetting the gypsies, who lost three million in the Reich's concentration camps), or homosexuals. In short, nothing compares to the Nazis.
And Sinn Féin deputies, of all people, should be aware that when they attempt to make any comparison, they are skating on their own very thin ice.