The problem with this kind of behavior is that it will encourage the forum to become an echo chamber, and will encourage others to agree with those who clearly have merit to spend.
That is one of the issues u have also noticed with users taking sides to try and get favour from higher ranked members
And some members use it as a reward for agreeing with them. (Some merit sources as well)
Meriting something you agree with is quite a task, but merits should be given you deserving posts regardless of your position, and point of view.
We might need a full guideline on how to merit posts and not just a few lines in the official rules.
I don't think it is appropriate to regulate how merits are given, especially if people are volunteering their time to give out merits. It wouldn't be fair that someone has to learn (and be accountable to) a bunch of rules just to give out something that doesn't have any benefit to them. You cannot 'unsend' merit, so someone who breaks a hypothetical rule would have a hard time remediating their mistake.
Aren't merits an overrated like button?
That is very much similar to what the merit system is. Although not all merit is given because the sender agrees (or "likes") the post, as a decent amount of merit sent is sent for posts of which a decent amount of effort was put into it.
Maybe for the next April fools day joke, theymos can implement a system in which people can award a "LOL" to posts they find funny, and an "angry merit" for posts that upset someone. People would need both merit and "LOL" in order to rank up, and if the "angry merit" to "LOL" ratio gets too high, their avatar will automatically change to a warning that the person is mean.