I'm not sure he ever 'hated' HalfBloods- only those who sympathised with Muggles. Even PureBloods like the Weasleys were labelled Blood Traitors for their sympathy for the Muggle community.

Good question

@The Dark Marc OK, hated might not be the right word but he said a wizard/witch with one magical and one non magical parent was an abomination

I can't recall the exact speech he gave- but I think you're refering the 'dinner' speech at Malfoy Manor, where Voldemort voices his disgust that a wizard might actually want to breed with a Muggle- and that idea was repulsive to him.

My understanding is that those who had been born Half Blood but hated Muggles were just as welcome to follow Voldemort as any other.

I suppose that his father was a muggle, and once he figured out that he left them (Voldemort and his mom) he gained hate for them thinking that every non magic folk is horrible.