There are two things I found valuable in the letter which is why I posted it:

First an example of a notable figure, known precisely because of the habitual strength of his reasoning, refusing to engage an opponent because of the repugnance of the opponent's values and insincerity of the opponent's participation.

Second despite the (clearly evident elsewhere) power of Russell's reasoning, his justification is exclusively emotional. He feels strongly about this and he stands by what he feels. He does not attempt to downplay this motivation or launder it through reason or rhetoric.

You're ascribing special significance to Russell having held a position, rather than the position's own merits, which is bizarre given how frequently Russell was known to change his mind. Had he outlived Mosley, I could easily see him having had a change of heart and regretting not having taken up Mosley on his offer.

And the dots, for me, remain unconnected. Are you suggesting Kirk represented such a radical, rightward departure from the Christian conservatism of (for example) Pat Robertson--a fixture of late 20th century American politics--that Mosley is a reasonable point of comparison?

Are you making a point about the protests in Britain, and not realizing that "refusal to engage," at least on immigration, is a major, if not the primary, reason why far right parties have risen in Europe and why Trump is in the White House again?