I agree that people tend to give them more to posts they agree with or 'like' but there's nothing we can do abut that other than try urge users to give posts for effort rather than you just agreeing with them or liking their point.
I believe that the meaning of merit is different from a simple like. Merit is deserved not by the post with which we agree, but by one in which the author consistently and reasonably expresses his point of view. You can agree with him, or you may not. But in any case, it isn`t just an attempt to write a constructive and useful commentary that deserve merit, but an intelligible and precise report of someone`s point of view. It is through argumentative statements between participants that a discussion can begin. Even if their views don`t coincide, but they explain them and prove, with respect to the contrary opinion and listening to the arguments of the oponents, the forum members will certainly discover something new. As we know, in a dispute, truth is born. And merit is worth giving to those who help to approach it, and not just those with whom we agree.