It's not very heavily moderated, but it does have moderators that can be summoned with the report buttons.

One of the first things you learn on SA is to "grow a thicker skin", because there aren't enough moderators with sufficient time to stop users from ganging up on some people and giving them a hard time. And as a result, moderators also allow a harsher tone.

The moderators are vital, but I wouldn't say that they are moderating heavily.

It does show the relevance of communities like SA versus random gatherings of visitors that most comment systems on websites constitute.