It's hard, really, to resist the urge, when you have a large fanbase, to use your popularity for political purposes.
Politics ARE important; people who refuse to acknowledge that don't realize how much an influence the big brotha has over your life; in addition, it's also about the right and maybe responsibility that you have to share what you think with a large audience.
Of course, there are those who shout out (especially right-wingers) that celebs who don't understand a darn thing about politics need to STFU and just stick to their area of expertise; to me, If you have the power to influence, you should do it. But give your audience a favor: don't bitch. Political commentary, like any commentary, needs to be constructive. If you post "this movie sucks; don't watch it", why should people trust you? You haven't explained yourself. The same is true of politics. Is your commentary contributing anything, or is it just bitching? Run this test before posting.