You're going backwards. The First Amendment protects a natural right which exists whether anyone else likes it or not. Saying an employer should be able to fire you is like saying the king should be able to evict you. You are separated from your living and made outlaw because you exercised a natural right.
There are a couple of fallacies with your comment....
first, nobody has made these people an "outlaw" thanks to......wait for it.....the First Amendment. Their comments, no matter how vile and evil, are not
illegal.
second, nobody is evicting these people from their homes over their comments...they're being fired from their [presumably private sector] jobs for being idiots. The First Amendment doesn't guarantee your right to work at a job even if the boss thinks you're an idiot who is negatively impacting their bottom line by your stupidity.