I suppose this is one of those juxtapositions - whether advertent or inadvertent - so I'll respond.
I didn't know of this person so I looked him up. He was ipso facto excommunicated by Pope John Paul II, although this was lifted in 2009 - he was excommunicated again in 2015. I have no wish to be excommunicated by way of some tenuous association with him. I haven't watched the video but he is known for talking down the numbers of Jews killed in the Holocaust.
Now, I don't think that the genocide of the Jews by the Nazis is a special case - genocides and ethnic cleansing are not infrequent events in human history, the first of which in the C20th was against the Armenians - but the Holocaust was the most well documented industrial example prior to the opening of the Soviet archives. The use of human abattoirs - in contrast to the usual methods of spontaneous
mass killing, exhaustion, dislocation and starvation - provided a shocking warning of the potential of the application of
scientific management to its perpetration.
I'll not get into the controversy that maintains that Communism is a heresy of Christianity and Nazism a heresy of Judaism which is, it is claimed, why the adherents of both were particularly vehement in their persecution of these communities. Thieves often calumnise their targets before their robbery - sometimes this is property, sometimes status, sometimes role, sometimes claim. The denial of the Holocaust does point to the fundamental evil of the program that cannot be contemplated even by those who are sympathetic to the movement that undertook it.
It is undoubtedly a historical fact and an essential one to contemplate given its ominous presence in human political affairs.
So that's the first response to Williamson but not the most important one in the context of this thread.
The second point is in relation to the practise of the faith, and especially for those who wish to worship in the traditional Latin form. The Church is a mansion of many rooms - that is why it is called Catholic. Those forms which were pronounced historically sound cannot be made unsound by tidal tastes. However, they should be practiced with acknowledgement of the validity of newer forms determined sound by the Prelacy.
An association with schismatics endangers the practice of the Latin Mass, not in the legitimacy of form, but in its use as a venue where antipathy is nurtured. This is the ground for its just suppression. Absent this ground there is no justice in denying its practice.
The same can be said of the
Cathecism - it is not suject to substantive revision, although it may
adapt in articulation. One has no more standing in abolishing the Latin Mass, or the Cathecism, or the Sacraments, than one does in abolishing the Doctors of the Church.