I learned long long long ago that the law considers a corporation to be a person, but the corporation is still a legal construct of a person. As such, can't the people that say in the law that a corporation is just like a person do what they want to define the ways in which the corporate entity can and cannot act like a "person person?"
That's an argument that doesn't carry a lot of weight with the current membership of the Supreme Court, which often tends to care more about the thoughts and feelings of legally constructed people than human people. But to me, we're starting to get a little into Westworld territory. Just like the designers of Delos created these robot people and watched them become minds of their own, the law has constructed the corporate person and ever so slowly it goes out of our control. And now Gunslinger has been unleashed on our political system.
This ignores the entire other side of the argument, which is the potential for corruption when campaign finances are unleashed. Person persons always claim not to do things because somebody's given them a free lunch or a nice pen. Which is the same way that most of us claim to be above average drivers, or to have the cutest baby ever known to mankind. Corporations spend so much money on political campaigns because, in aggregate, they get a return on their investments.
But even if that were not the case, even if we did live in some kind of ambrosian world where none of us ever did things because it benefited our bellies or bank accounts and were capable of being the ultimate altruists at all times, it would still make no sense to say that the very law which creates the definition of a corporate person can't put limits on how that person behaves -- and in fact put even tighter limits on the legally created person than on the real one.