I wouldn't want such a button.

Reasons for me are detrimental development of cliques as mentioned before and seen in many other forums but much more that public opinion would be more guided by the amounts of "likes" and subsequent answerds directed in this direction (can happen on purpose but more often it's subconcious). I like to trawl through posts and find many snippets I might not if the "right" i.e. popular opinion is guided (again, not necessarily on purpose but we just work that way).