A person who's drunk is divorced from his/her higher intellectual faculties and inhibitions. It may be true that what comes out when you're drunk is more or less already in there somewhere, but it's not really a person's "fault" when they're monsters inside--that's just something life does to you, and it's very commendable that the person keeps the monster under wraps when they're in a normal state of mind. You could blame them for taking the alcohol to begin with, knowing that they may become that monster, but on the other hand alcohol can be highly addictive / really hard to resist for some people and it's the only break from the constant emotional pain of their life..

We should always try to have compassion and understanding for everyone, and we should condemn nothing and nobody. It's not clear what "blame" means in this question, but it seems to imply antagonism/hatred/condemnation. And no, being compassionate and understanding doesn't mean being walked on by people, you can still express anger to someone for their actions, you can still take measures to protect yourself from them or separate yourself from them, etc. You don't have to hate someone to do yourself good.