but it seems on current evidence to be that a lot of people are mindkilled about whether or not politics is in fact a mindkiller.

Maybe the "mindkiller" business is largely a rationalization for the opposition to political discussion, and not the motivation for the opposition.

Some people like having their ideas questioned in a group, some don't. Mindkiller talk is a convenient rationalization for those who don't like it to pressure those who do like it to shut up.