Could be a very useful function if we customize such a tool properly. There's a lot of malicious content posted, that's true and much of it is also misleading readers. The Trust flags are only visible on top of a topic, if someone posts misleading content somewhere forther down the topic, no warning would be visible.
I made a quick visualisation and it's looking interesting:

For scam topics or obviously misleading content a demerit could actually be somewhat useful in my opinion.
If deMerit is introduced I would only grant users with let's say more than 500 earned Merit the right to distribute deMerit. Above 500 earned Merit every 10 earned Meit will result in getting 1
sdeMerit.
For example:
- an user with 554 earned Merit would have [5
sdeMerit
- an user with 702 earned Merit would have 20
sdeMerit
...
There will be no deMerit sources, deMerit is
only generated from earned Merit.
If someone's post is getting 1 deMerit, the Merit score of that user would be decreased by 1 point.
We could also argue that lower ranks can use deMerit but only 1
sdeMerit for every 50 earned Merit or similar.
Perhaps instead of these requirements, the demerit function could be restricted to moderators of the board, requiring only one press of a button. Just like how the reporting system can be used by anyone but only mods can actually delete posts. Newbies would start complaining about bias or "keeping them down" if legendaries were allowed to do this.
Personally, I would like it much more to have it as a community tool.
Bitcointalk is decentralized.

Demerit will not solve anything, a newbie with zero merits or -1000 merits will still be able to post crap if it fits his agenda.
deMerit would also be visible directly under the post like
Merit is highlighting good posts.
That way people would be warned against malicious content.