Corporations do have free speech. However, they have to deal with the backlash of their free speech. Example being, Chick-fil-a was openly opposed to gay marriage. For that, most gay people refuse to eat there. Corporations already have free speech but there will be backlash by anyone who opposes to that.
Freedom of speech is a cherished and even sacred right we as individuals must protect and uphold. Corporations however, are organizations of hundreds, even thousands and millions of people. They are not individuals who need their individual rights protected. They are organizations wielded by people for various social and economic purposes.