I'm well aware this is a completely public forum, yet I can't help but feel a bit as though the boss showed up to the water cooler while we were talking about him. I'd like to clarify that my comment wasn't intended to draw things off topic and towards your case specifically, but rather to express my general frustration with what I felt was being implied. I find the idea of presenting something as a counterexample without any consideration of the context to be rather objectionable, particularly when it comes to political topics.
To respond to the content of your post, while your list does cover the legal aspect, it doesn't address the broader topic of whether or not someone can be effectively fired for political activity (though I do appreciate that you in particular might not be legally permitted to address that topic given the current context). Unfortunately, when it comes to contentious topics the appearance at least is that people can often be forced out in one way or another regardless of what the law might say.
Regarding your item 3, and in relation to the broader topic of this thread, in the general case (not you specifically) it would not surprise me at all if someone failed to pursue legal action after being fired (or effectively fired) for political activity. Reasons that immediately come to mind include:
1. Legal action is generally quite expensive in this country.
2. Cases involving intent (hiring, firing, racism, sexism, etc) are notoriously difficult.
3. If the political view is even remotely unpopular, the risk of being run through the media may be unacceptable. Consider not just the general aversion most people have to public exposure, but also the impact on future job searches and other similar things.
As a practical example of your average person not wanting to deal with public exposure and controversy, consider the proportion of people who post to this very website under pseudonyms (myself included). Even if you only tally those who keep their posts professional 100% of the time, it's still most of them.