Vitor didn't cover all the details.

My original idea (which I retract) was that if you mark a post with a 'lastword' tag you are not only signalling that you will not be monitoring replies, but also clients that support this wont allow people to reply to it. That last part I think was my "ethical" lapse. I thought it was enough that they could repost it with any commentary that they wanted, as well as reply to the parent comments and extend the thread that way. Apparently that was an ethical blunder on my part.