You're in a country with no worker protection for that to be scary? And if you are, do you boss really care? Honestly I've read some scary stories about that in the US, but I often read it as FUD.
Almost all employment in the United States is "at-will" and you can be fired for practically any reason and with no notice.
> And if you are, do you boss really care?
The answer to this is, "who knows?" I don't want to spend an afternoon defending my tweets to HR, either way. There's a chilling effect. If even moderate opinions are risky, then I'm probably just going to disengage.