I'm not really for this, for similar reasons that I'm not for a dislike button here as well. Like if you're gonna agree with something, it's easy to like something and you don't always need to make any extra comments. If you don't like something, you can simply dislike it and not bother explaining why and just potentially look like an ass. I'm a proponent of talking to people about things, not ignoring them or talking at people.
I'm strictly speaking about like major things here, of course. Like if someone posted some political shpiel. Obviously this does have its good uses, like if someone posts that they're sick and you obviously don't wanna like that, but you'll be able to dislike it. lol But maybe I'm just thinking too much worst case scenario over the whole thing. :P