I think dislikes are a good way of creating echo chambers. This is a problem on Reddit. Certain opinions get downvoted for vexatious reasons and it deters people with similar opinions posting or contributing for fear of getting e-boomed. In extreme cases people will get discouraged and give up trying.
If you want to test this for yourself go to reddit.com/r/soccer and post something innocuous about how City haven't been found guilty of any of the charges against us yet. This is an objective fact, but your account will be swimming with the fishes in negative karma land.
At least if somebody actually criticises your post with words you have a right to reply and it can generate a constructive discussion. At the end of the day it's a forum, so think we should incentivise people posting instead of 'reacting'. I get the function of the like button, it has a sense of positivity and community about it. But I'd leave it at that.