For example, if I'm just chatting with someone at the park, I don't expect them to welcome a serious critique of views they espouse.
But if I've known that person for a long time, and we're invested in each other, then I'm more likely to challenge or at least discuss touchy matters.
Internet discussions, depending on the forum, tend to be somewhere in the middle. Being in a particular forum signals that people want to discuss certain topics. And anonymity allows a certain boldness, but it also means greater risk of being misunderstood or being treated uncharitably.