Because they think that the alligator will eat them last.
I disagree (at least in part). I think that liberals self-hate is at the root of their behavior. I think they hate themselves, hate the US, hate whites, etc. and think none of us deserve to live, themselves included. I know this doesn't include all liberals, but at least part of them.
I think you are right too, though. While they hate themselves, their thought process is flawed enough to never get to the logical conclusion.