Benedict Evans, though he lives in SV, would not have voted for Corbyn if he lived in the UK. Does Benedict Evans not know which political ideology is good for his own self-interest?
How do you explain away people who didn't vote for Corbyn because... they would prefer a non-anti-semitic leader? I have a hunch. You might say, "Well these people were duped. He isn't IN FACT an anti-semite." But, now the goal posts have changed and the discussion moves to whether certain claims are true, not whatever is in someone's best interest.
The thought that people you disagree with are simply fools because they don't know what is in their best self-interest, is not only arrogant, it's patently just not how the world works. Like always, it all comes down to whether your position or their position actually maps to reality. And if you think that you can't be wrong, or that it isn't likely that you get at least some things wrong, then your position is already hosed (not to mention lacks epistemological humility).