I leave it on because sometimes there's a comment which makes a salient point, isn't a dupe, and for whatever reason is dead anyway - maybe the user is shadowbanned, I don't know. I'd rather be able than not to see and vouch for such comments when they occur, but I certainly don't blame anyone for not wanting to see all the garbage that comes along with enabling showdead - which is most of what it lets you see, in any case.