I don't have kids, but my gut tells me that raising a kid is one the hardest things you could do. Trying to take care of someone who doesn't always respond to reason or logic day after day seems exhausting. I understand it when parents screw up.
That being said, I do think there are things a parent could do that go way over the line. Things that cannot be excused by exhaustion or frustration. Things like, I don't know, everything on this list.
Parents shouldn't threaten violence or teach them to be jerkwads. Do you know why? Because that is how we get violent jerkwad adults who teach the same bad lessons to their kids, and on and on the cycle goes.
Also, all the other reasons why you shouldn't be saying these things.