In real life you fear offending people you already know. For example I personally hate [insert company here] for multiple reasons, but I'm not going to express that in person in front of a friend or acquaintance I know who works there because it's likely irrelevant to the context under which I made a connection with that person.

There are routinely two groups of people I can speak total truth to, and those are (a) total strangers, and (b) very close friends. Online forums fall in the former category, as do random people who chat me up on trains that I know I will never see again.

Anything in-between requires some tiptoeing here and there.