I would be against this suggestion in its current form.

While I agree that most of the users affected by a 1-merit-in-200-posts restriction would be spamming newbies, there are bound to be false positives in there. I wouldn't be surprised if some of the denizens of Politics & Society and Off Topic such as notbatman or BADecker hit that ratio. While these users' views are (in my opinion) insane, we shouldn't be seeking to silence people we disagree with. I could also foresee a situation where people stop being helpful and responding to newbie's/simple questions, as they are unlikely to get merit for these posts, which is not something we wish to encourage.

A suggestion I did see in another thread, which I would prefer over this one but has a similar outcome, is charging users 1 earned merit per activity period (2 weeks) to display a signature. If they run out of earned merit, they lose their signature until they earn more.