Yes and no. That is true, but it's also possible, with white-collar work, for people to be fired "for performance" for pretty much any reason. That's the danger

Yes and no. That is true, but it's also possible, with white-collar work, for people to be fired "for performance" for pretty much any reason. That's the danger when you work on stuff where performance is pretty much impossible to define or measure. You have the legal right to disclose pay (except in a job with a security clearance) but most companies will isolate you, then make sure you get the worst work with impossible deadlines, document everything, ruin your reputation internally (though performance reviews that follow you if you try to transfer) and finally subject you to whatever passive-firing system they have around. I'm not saying that it's bad to discuss salary. You should figure out if you're getting a fair deal. But you do not want your employer to catch you disclosing salary. It will end badly.