Closing the loopholes will piss off corporations as much as raising the actual rate would. Those in charge of these companies will complain as much about closing loopholes as they would about an actual tax increase, so it's basically a lose/lose situation with these people.
The loopholes should be done away with, but I doubt corporations will be happy. It's to the point where all these companies need to do is sort of, kind of threaten to stop hiring, and taxes either stay where they are, or even decrease. It's ridiculous.