I’m pretty sure insults fall under free speech protection in the US, and in fact this case/law has been overruled by higher courts for this reason.
As long as you’re not committing slander or libel, you can insult anyone for anything really. And slander/libel is very hard to prosecute as you have to prove that the claims aren’t true and they they also caused tangible damage.
I was able to use Glassdoor just now with an account from there worked perfect