I think the worst thing about this is that once you hit the button, you wouldn't get any more replies from that thread. Is this really how it worked — that Gmail essentially shut you out of subsequent replies to the conversation in a non-undoable way? (Edit: Maybe you could revive the ability to get replies by un-archiving the thread? Does anybody know?) It just makes explaining yourself in the event of a mistake (and even viewing the fallout) that much harder.

It also looks like they put the button where "Send" would normally go. Mistakes seem inevitable; this is pretty mind-boggling.