When you are constantly put down and picked on and have no reprieve from that in your home life, you cannot be a functioning adult with the ability to decipher right from wrong.

I think Harry Potter would disagree- having grown up in with a seemingly worse background- abuse, neglect, not a single bit of love. Except there's no evidence Snape grew up in a necessarily abusive house, just that he seemed to have issues with his father which could mean a lot of things. Oh and he was poor, but once again Harry the same. Oh it's true Harry ended up with mentors and the like and actual friends, but that's because from the beginning he made good choices. From the beginning Snape made bad ones.