Why do they think people are less "judgmental" in real life? Do you think MN posters invent things for the fun of it? I don't.
People on here will tell you exactly what they think. Of course they won't tell you in real life - can you imagine yourself telling your neighbour/boss/colleagues/MIL what you actually think of them? What would be the point of that?
On MN, you have the version usually saved for your partner or your friends, whilst you keep a politically correct attitude, and at best try to express the same idea but in a very diplomatic way. Or what people bitch about behind your back.
You do also have very bitter people who tell you what they wish they had the guts to say but never will, that's true.
For most people, they just are polite but they don't think any less.
There's nothing brave in being very negative and "telling things how they are" in real life. It's usually unwanted. In MN, if people start a thread, they want to know... so they get their answer. Many don't like it!