Most corporations put their lobbying efforts behind or against legislation based on what's in their interest. I don't believe that the public can honestly expect them to act any differently so long as their behavior is in accordance with the law -- even if only technically, and even if the law should be changed.
I don't like SOPA one bit, and I don't think it should pass. I think what this highlights, however, is that legislation should stem from principles and the interest of the people (individuals only, please). This is not currently the case, thanks in part to a long history of Supreme Court decisions (culminating in Citizens United v. FEC) which permits corporations to buy politicians. It is certainly not in most politicians' interest to alter the status quo.
As with the Occupy Wall Street crowd, I say again: if corporations are following the law of the land in a way that's detrimental to the public, then the law is what's broken. In this case I'm increasingly of the opinion that all campaign contributions of any kind should be banned. In any case I'm appalled that the primary concern with sweeping and dangerous legislation is what will happen to the economy, and not the basis on which such a law is founded.