I'm afraid that you're just wrong on this. Read the 1st Amendment again. It doesn't say anything about a difference between individual rights and group rights.
The plain language of the 1st Amendment says what it says. You're interpreting it to mean what you want it to mean, and dubbing in something that it does not state.
If the members of a corporation want to put money toward promoting a candidate for office, or contribute to that candidate's campaign, then under our Constitution, they have every right to do so.
My wife and I, and one other partner happen to be a corporation of just three people. Are you saying that people like us should not have the right to speak out in support of a candidate, or spend our money to support them because we're legally incorporated?
That would be absurd. Where do you draw the line in your reasoning?
So do you write checks on the Corporate account to a politician? What if you and your wife want to give to one politician, and your partner disagrees? Would you just outvote him and give his money to someone he does not support?
That is why I say that only individuals should be allowed to give. I don't give a damn if it is a business incorporation, a charity, a union, or any other incorporated entity that plays with other people's money, they should not be allowed to give it to politicians. Period.