I'd prefer people to post why they support something, I think. Other than maybe tallying interest on major ideas, which can be done better by a poll anyway, it doesn't really provide anything beneficial other than maybe inflating the e-peen of someone who has a post that many people end up 'like'-ing.
Usually they also start leading to "I don't read the post, but I know the person so I'll click like", or people starting to ask "Hey, why haven't you liked my post", or whatever.
Usually they also start leading to "I don't read the post, but I know the person so I'll click like", or people starting to ask "Hey, why haven't you liked my post", or whatever.