I have worked at my job for 19 years. Do you believe the owner has the right to now change the terms of my employment and insist that I give up snow skiing, waterskiing, target shooting, hunting, my sports car, my beer-drinking and my occassional cigar, or else be fired?
I didn't say I agreed with the policy, just that it will happen. It's already beginning in fact, or we would not be having this discussion.
But I would agree that a partnership or sole proprietorship could fire you for any reason it chose. But a corporation, either a privately or publicly held one, is a creature of the State, and is thus subject to whatever limitations the State might choose to apply to it. Of course the State is a pretty stupid beast as well, and may (will!) exercise it's powers unwisely. But it does have those powers over corporations.