Don't want to get too off topic here, and I like your enthusiasm, but I would disagree strongly with the implementation of such an idea.

Merit is already treated by many as a "I like this/I agree with this" button rather than a "This is a constructive post/This adds to the topic at hand, regardless of whether or not I agree with it" button. A de-merit button would be treated the same, with many users using it on posts they do not like or disagree with, rather than posts which are simply spam, zero value, etc. There is no doubt people would use de-merit against users who accuse them of something, give them red trust, or simply disagree with them. I also have no doubt that there would be merit circles who would conspire to heavily de-merit users they do not like.

Having such a set up essentially turns us in to an echo chamber like Reddit, where the most popular opinions are the most visible, regardless of whether or not they are actually correct.

We already have (multiple) rules against this sort of behavior from BADecker. We just need to actually enforce them.