That would get you banned, I suspect. And how is this different from the previous system? If users found harassment and trolling funny, they could rate it up in the old forums too. It's also still possible to ignore users if you dislike their posts that much.
If it were that blatant then I agree, it would probably get me banned. But a more subtle variation most likely wouldn't, because banning someone is a blunt and heavy handed punishment; you either broke the rules and are forcibly removed, or you're not. There is no measure of degree. You can't just ban someone for being chronically stupid or unhelpful. As for how this is different from the previous system? I would think this would be obvious. With a downvote, users can "punish" me for my rudeness, which in turn drops my rating and can push me below rating thresholds that many users use when browsing the forums.
I guess the moderators responsibilities include moving threads around and maintaining specific FAQs and probably other things; I can't find an FAQ that details the moderators job description. However, to a large extent I think applying certain standards IS part of their job (at least, that's always been my impression) e.g. closing threads which become abusive or contrary to the gamedev rules / terms and conditions, as well as dealing with users who break those. This happened in the old forums.
Yes, it's the mod's job to enforce de jure rules. Is it also their job to enforce the de facto standards of the community, which are far more flexible and can fluctuate rather quickly? How would the mods even determine these "community standards"? In the old system they are an amalgamation of everyone's opinions, not determined by any one person or group of people.
I feel that some things could be better about the new user rating system: ratings could perhaps be more visible, and individual posts could have down voting. However, I think it's rather extreme to say that because users lack down-voting, standards of posting will suddenly drop. If you want to maintain standards then make useful posts, and encourage others to do the same. If users are motivated to do this by a number, that's great, but if they're not I don't see why they would care any more about down-voting than up-voting.
I'm not bothered by rating based on post. It was an oft-requested feature of the old system, and it lets you see which of your posts are making a good impression, and which aren't. Without a down-vote to counter up-votes though, they basically lose all meaning. As for why they would care more about down-voting than up-voting? Well, down-voting implies the loss of goodwill built up from previous work. With only up-voting, there's no need to worry about individual posts as much, since they can't ever
hurt you, only help. You can throw out posts here and there without thought to how they affect the community's image of you as a whole; unlike in real life where
everything you say will be held against you, for good or for ill.
But you ignore the problem with the old system. That a rating specifically designated to indicate helpfulness and technical knowledge could and was (no need to experiment there) lost for things unrelated at all to helpfulness or technical knowledge. It also had the problem of not being on the same page as the posts themselves, which has it's own bag of side effects.
I think this is a common misconception; I don't think the old rating ever denoted only technical competence, nor was it meant to. It simply stood for your reputation in the community. Each person has some opinion of you, and an idea how the rating system works, as he sees it. If someone decides that he will rate down people with poorly written posts, he's completely within his rights to do so, and your rating will reflect that little piece of his opinion of you based upon that. I know that personally I find language debate threads to be incredibly asinine and inane, so very often starters of such threads would find themselves rated down based upon that. It lets me express my opinion of such threads without requiring moderators to step in and ban people. I may not like such threads, but I don't think users should be banned for starting them either.