A " dislike " is an invitation to bad mood on forum. Rating a thread in terms of likes received is much more easier.
So if someone keeps trolling and/or spamming (which might be rule-compliant if your rules are too loose), the worst thing the users can do to him is not rating his postings? Really?
That's why I actually suggest an add-on: that's plain stupid to me.
So you're suggesting a Reddit-style self-regulating system when a post can be upvoted or downvoted and is hidden by default when it receives too many downvotes?
I'm suggesting an optional module ("add-on") which adds negative ratings to the positive ratings and allows every user to decide if he wants to see negatively, neutrally or only positively rated postings per thread, so I'm, more or less, suggesting something slightly more sophisticated than reddit's "everything or nothing" system.
Sounds something like the xenforo post rating plus filtering ability based on "type" (i.e. positive/negative/neutral/whatever) of rating.
It would be interesting indeed to see!