Chris: 'You say yourself here that the reasons he may have made the propositions don't affect whether they are true or not.'
Yup. That's what I said.
The essential proposition is false, by the way. History is a process with a subject (many, in fact). And there is a relationship between his beliefs, and his practise: His theory was an otiose aplogetic for Stalinism, and a polemic against human agency.
But no, in itself, the fact that he was a shit, does not itself prove the theory shitty. But it was.