Ok, so your view is predicated on the various privileges afforded by the corporate charter. I get that, and tend to agree - although I'd prefer to fix the problem - the corporate charter - rather than the symptom.
What about privately owned businesses? Do you think they should be allowed to engage in political activity?
We keep churches out of politics, I fail to see how this is different.
It's not different. Keeping churches out of politics violates the First Amendment.
Are you saying that non-corporate private business should be prohibited from political activity too?