But it seems to me that a 1 merit / 20 posts can't possibly be a difficult task unless you're a complete shitspammer... Thus you shouldn't be allowed to write.
Most members don't fit in that, and it is not an an indication of quality posts by any means. your idea will help fight shitposting but it will also stop good posts when everyone is paranoid of not getting merit,therefore running out of posts. the knowledge sharing on the forum will drop along side with the shitposting.
there are also many off-topic posts and market place that supposedly go un-merited for a simple reason.