Liberals find repellant the idea of insult*, not because they refuse to be crass or impolite–they are perfectly skilled at being both–but because to say that something is bad and outline the traits that comprise its badness is to say that one thing is better or worse than another thing and that there are certain traits which are, inherently, better or worse than others. Such judgmentalism does not jive with the quest for full equality–equality of spirit, body, and soul.
*except against personal enemies
There’s one strain of thought which holds that liberals (and perhaps conservatives) are a specific ideology that has been transmitted over the centuries, and another that liberality and conservativeness are just personalities that people happen to have.
A related quote:
I tend toward the personality hypothesis, and that society needs both liberal and conservative personalities for optimal functioning (one side is good at generating novel ideas, and the other side is good at preserving things that shouldn’t be changed,) but this is dependent on both sides recognizing this and letting each other be. (Ideally, this is where something like federalism comes in.)