And, to be perfectly honest, I do not necessarily see this behavior as willful. Some people are just like this. But some people are just child molesters and serial killers too. Personal responsibility or punishment doesn't enter into it. There are just certain behaviors that need to be removed from any community for the general health of the community.
The primary thing to watch for is fallacious arguments. Especially the straw man fallacy. The idea is that, instead of beating up your opponent, you set up a "straw man", beat that up, and claim to have beaten you opponent. In debate it generally takes the form of falsely attributing an argument to your opponent that they never made. Like I might say, "I really don't agree with your contention that we should kill babies."
Your automatic response is to say, "hey, wait a minute, I didn't say we should kill babies." and you are instantly on the defense. Suddenly you are spending all your time defending yourself against false accusations, usually worded just close enough to what you are actually saying to sound almost plausible. This is actually a very subtle form of ad hominem attack, meaning attacking the person instead of the point.
This is a verbal dirty fist fight. The object isn't to get to the truth but to wear down your opponent with trickery and emotional and mental traps until they either give up or melt down in frustration. Some people are extremely good at it and very subtle. You find yourself fighting against pretty much nothing, like boxing with a ghost. There was a community here years ago I used to watch where the whole point was to debate using fallacy. It was very educational.
Another is arguing without substance. Things like, "There are many fundamental flaws in what you are saying" without naming what those flaws are. You have been challenged and told you are wrong, but not how you are wrong. Or something like "statistics lie" to refute some statistical evidence without saying specifically how or why the specific statistics in question are wrong. Again, when they present a negative argument with no real substance that you can actually get hold of to debate against, then that is fallacious.
You just waste your time arguing with empty air because as soon as you answer one fallacious point they just present another. The advantage of fallacy over legitimate points is that there is an infinite supply of fallacious arguments in any debate. It becomes a never ending debate where you are always on the defense and no one can stand up to that.
The moderators of a community are particularly vulnerable to such attacks because of the added argument they can throw out that "you are just banning anyone who disagrees with you." But, I think most community moderators are even more hesitant to ban when they are personally involved. And I think most trolls know that and try to take advantage of it. I tend to look very hard and give the person every opportunity to actually make a legitimate point when I am personally involved.
But in the end, I have to make a call one way or the other. And I will always make that call based on what I think is best for the overall long term health of the community. That isn't always easy. I may not always be right. None of us can guarantee that. But I have to make the call. And if I think someone is arguing just for the sake of arguing, they are out.