OP did something dishonest by making the title and body TOTALLY different, in my opinion.

The title is why are people hating on him. Lots of good answers to that.

The body then switches it to wanting him dead. I don't think very many people want him dead. I think even the CIA/US Government want him alive and in jail rather than dead.

edit: I also think you were implying that disliking him was the same as disliking the idea of whistleblowers generally or wikileaks specifically, though you seem to have walked that back. It definitely doesn't, though the fact that wikileaks is cowed by dictators like Putin is definitely a red flag when compared to their stated mission.