Protesting publicly is one thing. Talking in your own kitchen is another. I guess some unlucky people got busted for that, but generally it was safe, as long as no one deliberately ratted you out (which didn't happen much since Stalin died). And even then, circumstances needed to be really hard against you.

Also, it obviously matters what it is you're saying. Most people just told jokes about the communist regime and talked about how shitty life was. Nobody cared about that as long as they kept it private.