While this is for a good intention, it may makes things more difficult for the forum in general.

The rate of earning merit as a newbie is really difficult that I think even on average making 20 posts doesn't guarantee merit and such a user might not be a spammer rather trying to contribute, learn and others which include what you added on your post about those coming to make complaints.

Also, this will lead to even more eagerness  for wanting merit, making not just spammers but more merit farmers neither of these are good for the forum growth.