Some users have suggested that a up vote could be introduced which would show that they appreciate the post but, don't think it's worth a merit. The only thing with Stack exchanges system it wouldn't likely work at this forum. Stackexchange is primary used for asking and answering questions. But, this forum is much more complicated than that, and there's probably no real incentive of having an alternate account on stackexchange where here there's multiple reasons why someone may have an alt.
This opens the possibility of abuse, but not only from alt accounts. A lot of people have made a lot of enemies around here specifically those who point out scams and would be targeted by these down votes. This is also why a lot of people including myself are against the idea of a demerit.
I think if we ever introduce a system like this it would have to be limited to a 'like' and you could like a post. Honestly though, I don't think it's a big priority and there's probably better things to worry about.
I did not mean to replace or adjust the merit systems using votes or likes. These two systems would opperate independently. And I recognize the difference between a discussion forum and a "support" system (which the Stacks are).
As for demerit, I don't favor that either, but included it as it was suggested in other places.
However, I did not consider the issue of alt accounts. This adds of course an interesting twist.
From your comments I take it that you don't think there is anything else that can be considered (aside from the merit system) that would increase the quality of the discussions? It would be disappointing if the quality issue is just a fact of life which simply has to be accepted.