It was a shitty swipe of a comment, guaranteed to provoke a flamewar. I didn't react to it because I didn't see it. That's the likeliest explanation in general, when you see a post that should have been moderated but wasn't.
Dang, the individual you were replying to, is the lead moderator. (dang is his first name and his initial -- Dan G. The G is for Gackle) The moderators are routinely accused of censorship, of single-handedly suppressing articles that the broader membership flagged off the front page, etc.
It takes more than one flag to kill an item. I think there is a karma threshold for flagging, so -- iirc -- no, simply having an account doesn't allow someone to flag it.