However, I still think it would be fun to have an option to turn merits off when creating new threads. Could be useful if a thread creator wants to dissuade posters whose sole goal is to obtain merits...
What about the ones who are actually making good posts in a thread where merits are off? I don't think it's reasonable to disable merits for everyone in a thread only because a few users might try to get merits by any means. Besides, the ones who are giving them merits must think they deserve it, and merits are not moderated, as far as I know, but that's not the actual point here. The point is, it's an injustice to those who actually make good posts and deserve getting merits.
Since the merit system is centralized, there's always going to be some level of personal opinion and control that users just have to tolerate. Still, completely disabling merit in a thread feels like punishing everyone for the actions of a few. It's better to address merit abuse directly than to limit the ability of genuine contributors to be recognized and appreciated.
A more viable and reasonable solution, imo, would be to deduct merits from a user's profile/account if they have got them in a self-moderated thread, and their post got removed by the creator of the thread.
I suggested something similar before, but I said it should be done even for deleted posts from moderators, but since we are discussing this issue, I think it's at least a good solution for this problem.
Now, if something like that is applied, users who don't want merit abusers to come in their thread, and try to obtain merits, and if that happens, and abusers get merits for posts that the creator believes don't deserve it, the posts should be removed/deleted, and the merits received should get deducted from the receiver's merit count.
Engagement in self-moderated threads would likely drop significantly if such a rule were implemented. Lets consider instances where users with valid but differing opinions from the thread creator might hesitate to post, not only because their replies could be deleted, but also because any merit earned could be revoked. This creates a poor effect on open discussion. Every suggestion has two sides, and often, those who push for stricter rules end up being affected by them eventually.