No, they are allowed to, but it is my right to think it is just shit behaviour to turn on anthing he has a minor involvment with but has no connection to his views at all.
I think that without "those that oppose Jon" [and specifically, that subgroup that is now starting a discussion about Yooka], Yooka would be completely uninvolved in any controversy. In that sense, "those that oppose Jon" are more culpable. Now it's a different question whether what Jon said is worse or what is starting to happen to Yooka now is worse and if my first impresion of what Jon has said is correct, then this is undoubtedly what Jon has said. I have no problem with complaining about what he has said and discussing future involvment in new things.
I think that the associated pressure on changing a finished product for a minor involvment of someone who has in the meantime said something objectionable is excessive and to the detriment of years of work of a dedicated team of talented developers, putting the focus, in crucial phase of time on something so minor, instead of the product itself.
He is not a decision maker for Yooka-Laylee. Fighting ideas that you don't like is one thing, fighting unrealted (to those ideas) products someone having an idea you don't like might have a minor involvement with, is a totally different thing.