Arshes: I do think comment hiding is a stupid idea, for the reasons you mentioned and more, but I was just pointing out that there aren't any technical hurdles in implementing it. ...Well. I'm sure we all remember what happened in old-fa when the admins started deleting newspost comments all around. But that was just bad coding.
Mottenfest: The idea here is that there should be a fossil record for all comments, be they insulting or complementary. I personally think the blocking system is stupid, but I can see wy people use it, and I'm okay with because it's not retroactive. Deleting or hiding comments could create gaps in the fossil record, which is bad-- you wouldn't be able to tell if a user had been, say, hiding all comments giving artistic advice, or all comments from anyone not in a personal circle of friends, or other kinds of abuse like that.
On a totally unrelated note, oh my god is it weird to go from writing XHTML to having to deal with the stupid bbcode. I wanna <q> things.
