Legally, it does not prohibit you from being intolerant as a private citizen (it is another story if you are acting as an employer or in a place of work, of course). But my point is not about legality. It is about what is ethical. Something can be perfectly legal, but not ethical. We all have the right to be ********, bigots, and duchebags. The first amendment is a big player in this. My point is that these protesters exercised their right to be bigots as private citizens. I am asserting that what they did was wrong on ethical grounds, not legal grounds. The man in the OP exercised his right to donate to a particular political agenda. From what I understand, he did so as a private citizen, outside of any leadership role he may of had and before he took the position referenced in the OP. It does not appear he was planning on enforcing his agenda in the workplace either. In this context, I see the actions of those calling for a boycott to be (while still fully falling under the 1st amendment) an act of bigotry comparable to the same bigotry they claimed to be opposed.
Essentially, both the actions of the (ex) CEO and the boycotters in the OP were legal. Yet, both were equally unethical.