Before we spend too much time attacking Facebook over this, let's try and think of possible reasons why this
might be not an "evil" move. No need to go out of our way to conclude "omg they're evil stealing our privacy".
Firstly, what if they just don't want to confuse users? I see people confused all the time of when you need to click and when you need to double-click, every time I see someone using the computer — I'm sure I do this myself, too. What does allowing someone to introduce uncertainty as to what's required here do, especially when their click-through buttons look just like Facebook's normal ones on other sites? I'd say it'd just confuse people. I don't have an issue with Facebook doing that, I'd actually rather have them enforce, this, so you know what is going on when you see a standard Like button.
(As a few other comments have noted, just replacing the button with a custom-styled one would solve this issue. It'd also solve user confusion, since it no longer appears to be Facebook requiring a double click.)
So, maybe they're not just after destroying privacy, after all? Maybe?
(I don't work for Facebook, or even know anyone who does. I just like to try and see both sides of something like this.)