Abolishing corporate personhood altogether, so that we wouldn't be able to maintain the useful legal fiction of the corporation for purposes like listing the owners of property on deeds, doesn't strike me as either a good idea or one that has any likelihood of becoming policy. But I'm happy to see a movement that might push policy a small distance in this direction. The majority of the people in any movement that pushes for good changes on a complex issue will have confused views about matters of detail. And this is a movement one should support.
Much of the reasoning in the Citizens United decision is based on the failure to recognize that the notion of the corporation as a person is nothing more than a useful legal fiction to be maintained when it has good social consequences and ignored otherwise. Bainbridge offers consequentialist arguments in favor of giving corporations some legal status. Even if these arguments are good (as I think they are) I don't see how they can support striking down Congress' judgment about where the good consequences of corporate personhood end.
When Scalia writes that the text of the First Amendment "offers no foothold for excluding any category of speaker" the obvious response is that the text may offer no foothold for excluding any category of real person who may want to speak, but that this doesn't cover what we call persons in some contexts merely as a convenient legal fiction. The real / fictional distinction is among the deepest distinctions there are, and Scalia's attempts to elide it are ridiculous. Our claims typically don't encompass fictional entities. When I say that hobbits don't exist, I'm not saying Frodo isn't a hobbit, or that you're doomed to fail at pretending you're Sam Gamgee for the purposes of Live-Action Roleplaying. My claims encompass only the real. And that's the right way to understand the claims about rights in the Constitution. Real persons have rights, but if you're just pretending that something is a person for limited practical purposes, you don't have to pretend it has all the rights persons do.
I hope it's obvious to Bainbridge and Scalia that corporations shouldn't have the right to vote in elections after they've existed for 18 years. The end of a corporation isn't a death, such that intentionally causing it would be murder. These points follow just as well if one sees corporations not as fictions but as groups (as Scalia does at some points) -- groups don't have the vote in addition to that of the individuals who compose them, and disbanding them doesn't constitute murder. If you ignore the distinction between convenient legal fictions and real entities and regard corporations as fully real persons with genuine rights, I don't see how you draw these distinctions.
This is what the opponents of corporate personhood understand. If they're wrong on the details, they make up for that by having a grasp on the fundamental issues.