This is probably the longest-running debate in human history, and he dismisses it completely with a link to his undergraduate paper on the subject.
Putting that aside, the problem with this argument is it doesn't allow for changing beliefs. If we are only driven by fitting in with our group, then no political views would ever change as they wouldn't ever reach critical mass.
Just look at the changing opinions of gay marriage. Political views absolutely do change over time, and they can change very quickly. Yet this paper is all about how that is impossible.
> I have witnessed few political conversions, so the most I can offer is speculation as to how one might occur.
I feel like this is an admission that the paper is entirely speculative.