I feel a little funny when they speak out, because of the larger context in which this happens.
Our culture over-idolizes movie stars. Heck, the most popular episodes of game shows like Jeopardy and Who Wants to Be a Millionaire are the "celebrity" versions, and those are the worst shows, because the celebrities are worse players than the typical contestants.
Being famous as an actor does give a person any special expertise in other areas, whether it is game shows or politics. And so, I feel a little uncomfortable when a celebrity takes a political stand with the expectation that his or her statement should carry special weight because they won academy awards.
I guess it is more the way the culture responds to celebrities that bothers me, rather than the celebrity taking a stand the way anyone else is entitled to. I don't see why one's status as a famous actor should give a person more of a mouthpiece about political and social issues than other people have, or that we should take their words as having any special authority.
On the other hand, you mention money, and that is a different matter. If a rich person, including a Hollywood star, donates a good deal of money toward a worthy cause, I do commend them for that. And some, in addition to donating, have actually researched the situation and DO speak with some expertise, and I respect that as well.