Why do forums never allow 'dislike' compared to 'like'?

Mike-B posted:

Eloise posted:

The Like is a good idea ... better than forums where threads are continually littered with posts which just say "+1"

Nigel the Halibut has banned +1's,  those found guilty will be sentenced to listen to the entire Justin Bieber catalogue.  

+1 

One of the many reasons I am not on Facebook is because it seems to me you are forced to 'like'.  Facebook is like the play school yard, if you want to make friends you have to be nice.. Its seems like so much unecessary tedious work, while on forums you can like and dislike (providing one is civil and polite about it or disguise it as exchanging of opinions or ideas).