Should it be an "unlike" or "dislike" button on Facebook?

I see an increasing demand for an unlike button on Facebook:

• http://www.facebook.com/pages/The-Unlike-Button/72641866357

• Facebook Adds An Unlike Button For Pages
  ^{May 7, 2010}

• Facebook "Unlike" Button Comes to the News Feed
  ^{NOV 3, 2010}

I have always used and understood unlike in the sense of dissimilar. Is it ever used in the sense of do not like?

Solution 1:

"Unlike" in this case refers to the fact that you have "liked" this post, and now, due to a change of opinion, you decide to reverse that "like", by "un-liking" the post.

"Dislike" is not used here because "dislike" does not have the same effect that "unlike" has. "Unlike" is used in this case only to remove a "like", but "dislike" has the effect of not only removing the "like" but to actually have feelings of antipathy towards the post.

Putting it in SE style:

You see a post you believe is good, so you give a +1(like). After a while, you change opinions, so you remove your vote(unlike). Then, you think, this post is really bad, so you give it a -1(dislike)

Solution 2:

In the modern world, and particularly in the world of computers, the un- prefix is increasingly used to denote an opposite or reversing action.

As in install/uninstall, register/unregister, and delete/undelete. Not to mention the undo facility we rely on in many applications.

In short, people quite reasonably expect the Facebook functionality to be called unlike because that follows the pattern they're used to. There's no danger of confusing such terminology with the dissimilar meaning, so why not?