The general argument I've seen has been that Proposition 8 was "just an opinion" or "just freedom of speech", while the people speaking out against Brendan were "a lynch mob", on a "witch hunt", an example of "lefty liberal intolerance", etc. etc. etc. etc. etc.

So the people making the argument typically need to have a position where Brendan supporting Prop 8 was not bad, but Brendan being called out/pressured to step down over it was bad, because for some reason they need him to be a victim of "bullies" in order for their worldview to work.