Professor Volokh, in the wake of Citizens United, takes on the "money = political speech" interpretation of those who dislike the majority opinion:
It's that restricting the use of money to speak, like restricting the use of air travel or computers to speak, interferes with people's ability to speak. One can debate whether this interference is justified. But mocking the pro-constitutional-protection position as resting on the notion that "money is speech" strikes me as quite mistaken.
His co-blogger, Ilya Somin, parses the "corporations aren't people" argument:
I'm not arguing that corporations themselves are "persons" with constitutional rights. Rather, I'm asserting that their owners and employees are such persons and that that status enables them to use corporations to exercise their constitutional rights. Similarly, partnerships, universities, schools, and sole proprietorships aren't people either. But people can use them to exercise their constitutional rights, and the government can't forbid it on the sole ground that they are using assets assets assigned to "state-created entities."