Corporations and Taxes

I have always heard from the GOPers in my family that corporations should not pay taxes, due to the fact that those profits are already being taxed via the individuals tax payment. At least that is what I believe the argument is. However, due to the recent Supreme Court ruling in Citizens United it would seem to me that this argument not longer holds water. In that Supreme Court case the justices decided that corporations are people and-in this case at least-are entitled to spend whatever they want to on political campaigns because to deny them that right would be a violation of the First Amendment's free speech protection. Thus if a corporation is a person, and a person must pay income tax to the federal government, then it should follow then that the corporation should also have to pay income taxes to the federal government.