I've never known a strong business that cared if employees mouthed off about management or the business.
I had one employee in particular who talked behind my back constantly. I had zero problem with it. He was doing a great job for me; why would I care about anything else? He invited me to his wedding, we've exchanged Christmas cards for decades, and I recently talked him into a retirement job trying to turn around an academic program. Another guy who talked the business down, outside work, has gotten outstanding references from me for thirty years. He earned those references. Beats me why someone would want to limit or control what people do & don't say about work - outside of passing trade secrets, obviously.
UNLESS they're trying to maintain a bullshit fake image of how the business is going, which most adults recognize would be futile.