Yes, corporations have a right to free speech and to spend without limits in elections, because the U.S. Supreme Court has decided that, for the purposes of free speech, a corporation has personhood. That means, they have a right to say what they want to. Elections have a big impact on corporations, and they should have their say.
There's been a lot of talk about corporate personhood in the last several years. Especially from corporations who argue passionately that they have rights. I'll believe that a corporation is a person when a state sends one to prison and executes it. And until that happens, I don't think they have the right to free speech or unlimited campaign donations.