Agree with this! If we're to try fighting against shitposting and spammers - there must be a REAL punishment for villains action. Merit is good and everything, but the fact is it doesn't help in this particular case due to no mechanism of lowering it as punishment. It serves its role in highlighting quality posts most of the time, but does no good in preventing or eliminating the shittiest ones.
IMO, there should be a 'bad' bMerit either as a separate stat, or interchangeable with merit. Interchangeable is the hard thing though, the control at the beginning would be in high merit accounts hands, which, unfortunately, seems as a bad option given the merit abuse going on since its inception, as well as the fact that nothing prevents them in using it in a self-serving scenarios. Separate stat, for example red 'Shit Post" button near every post , appears to be much more reliable and decentralized in concept as well. Provide all the bitcointalk users with button charges depending on rank(i.e. 1 daily charge for newbies, 3 for Jr.Member, 10 for Member, then 50, 200, etc...), limit the amount of charges available for use by single user on a single post by 1(this could be rank dependent as well, but not necessary, as the more flat it is among users, the more decentralized the whole concept is) and  all you have to do is add "Shit Post" counter rules automatically applied for users. Rules could be something like 20 charges on a single post - user gets warned and asked to modify/delete the post, while at 30 post is auto deleted and user gets 2-3 days ban from that particular subboard, 120 total charges on  all your posts across the forum in last 7 days - you get banned for 1 week. 300 in a month...?  Month ban is provided for free! This way the more important/popular/high-level the discussion is, the higher the risks are for the shitposting villain, while newbies can still post trashy comments/questions in their own boards, where the daily charges limit would make it very unlikely to be banned for minor stupidity(1 daily charge among most participants would lead to users awarding only the most retarded posts with their precious charge).
This change would lead to a more self-regulated forum, freeing existing moderators time for more relevant issues, giving individual users a non-abusable moderating role and cleanse the forums of most filth.