If you really went back, you would have found lots of personal slams by all 3 banned posters. If you look further, you will find that there have been and are posters well read and respected by most of us on TOD who have views consistent with H****'s and even possibly F***'s for example in terms of peak dates. Khebab, Rembrandt, RR, Euan Mearns, Skrebowski and several others have the same view of peaking dates for example as does H*****r, but have engaged in a long-term, civil, mutually respectful debate with Westexas, Dave Cohen and Stuart Staniford who believe peak is here.

I think, therefore, it is obviously not the opposing views that got them banned. I think the right decision was made. I hope Dave will stay. I am sorry we lost Freddy, because he did have a contribution to make, but he also was extremely rude and derogatory too often, which detracted from his own points.

Dealing with opposite views in a democratic and fair way is a touchy subject. I'm also a moderator on PO.com and appreciate the difficulty of moderating a forum. I agree that it takes courage to preach contrarian views on any forum. Try to preach Darwinism in a creationist forum and see what happens! Everybody will dismiss your views and you will get very frustrated very fast and may resort to ad hominem attacks to get some reactions.

IMO, in any public arena, if you have contrarian views and want to convince people it's up to you to make high quality comments, backup your claims with references and be as civil as possible. I think TOD should have zero tolerance on any ad hominem attacks from any posters. The best would be to have some sort of comment ranking/filtering system in order to filter the noise.

if you have contrarian views and want to convince people it's up to you to make high quality comments, backup your claims with references and be as civil as possible.

No, this is most often ineffective, see Controversial Dialectic.
Therefore I disagree with this:

I think TOD should have zero tolerance on any ad hominem attacks from any posters.

The problem isn't ad hominem or whatever "political correctness" it is EFFICIENCY, the banned trolls weren't efficient they were clumsy and undermined their own positions, they rightfully lost, I am NOT supporting them.
I only want to emphasize that your suggestion is misdirected.

Interesting, however how do you evaluate a poster efficiency? maybe (total valuable information)/(number of comments).

khebab, I do love the way you think.