I think SOPA is an unconstitutional, dangerous waste of time - that is, a violation of the First Amendment that won't achieve its ends, and could cripple the Internet with its provision that sites could be liable for any pirated material posted on their online premises. No site can possibly police every post - text or video - for adherence to copyright.
Wikipedia actually does a pretty good job of making sure every image on its site violates no copyright. But I think Wikipedia should not shut down on Wednesday to point out the danger of SOPA.
Wikipedia is a source of information, a site which by its very existence stands up to ignorance in Congress. It won't be able to make this point on Wednesday when it's shut down. And in doing so, Wikipedia will inconvenience millions of people, including students of all ages, who rely on its services.
Wikipedia could make the same point by putting up a page about SOPA which everyone who goes to Wikipedia would see. A page like that will indeed greet people when they try to go to Wikipedia on Wednesday. What is gained by then preventing them from getting the information they're seeking?
In times of revolution, even just in opposition to authority, it is especially important that lines of information remain open. The world will survive Wikipedia's day of darkness, but it is a wrongheaded, unnecessary move, and SOPA will be defeated without it.