Thiel's support of Trump shows that Thiel is a sexist and a racist. If YC wants to attract startups with founders who aren't white men, this is a problem. If startups in YC want to attract employees who aren't white men, this is a problem.
Maybe. Who knows. You should ask him. Pretending to know why he votes for Trump is just wrong.
You assume what he thinks, his state of mind, etc.
Idunno, maybe you should consider accepting that supporting a person does not equate to being that person nor does it imply that both hold the exact same beliefs.