I don’t know what the big deal is. It is absolutely okay (and legal) to fire someone who disagrees with you politically. If I owned a company and someone showed up every day with a Biden or Hillary or Udumbo sticker on their car, I would likely fire them. There is no right to free speech in a private setting and political beliefs are not protected under the Constitution. In most, if not all, states you can fire anyone for any reason unless they have an employment contract or they can claim you discriminated against them based on race, sex, age, or religion.
That's what you CAN do.
But should you?
I think what we're seeing is a set of companies firing good workers because -- perhaps 5 years ago -- the worker said something on social media.
Yes, you CAN fire someone for that. But SHOULD you? What kind of country are we?