I agree with this too and perhaps Dumbledore is half blood or muggleborn which is why Snape realised that not all muggles are bad (maybe).
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You're almost on the same page as me. I'm saying that Snape has been a good guy the whole time, not that he was swayed by DD to be nice to muggleborns or whatever.

Snape has merely distanced himself from Harry so he can help him right under Voldemort's nose without either Voldemort or Harry ever knowing. By making Harry hate him like that...knowing that Harry never mastered Occlumency...Voldemort will never doubt Severus' loyalty, even though he's helping Harry to destroy the Dark Lord.