These "other users" you speak of... a couple of them perpetuate the cycle and so the farmers return, like a festering plague. To be fair, sometimes people (myself included) don't even realize they are meriting an account farming weasel (and you probably don't even like their other accounts) until its too late.
All true. But I don't think that's enough to kill Merit in that thread.
Now that I think about it: Merit could be isolated there: I often see "+1 WO Merit" written in that topic. This could actually be made into a thing: WO Merit that only shows in the WO thread. Users could even have different ranks there than on the rest of the forum. And now that I type it, I don't think it's very useful (but it sounds fun).