The distracted pilot who leaves the original QNH set and then decends to what he thinks is circuit altitude (say 1500ft) would be in for a nasty shock.
I'm not convinced. When I fly to an airfield and have no local pressure setting, I look out of the window. If the trees look close, bad
...Seriously though who uses the altimeter when landing? I use it to get setup at circuit height but if it wasn't there I wouldn't plummet into the ground just because...
I would actually like to suggest that I could safely fly across country VFR with no altimeter at all (assuming no airspace and nice weather) and still manage to take off, cruise and land with no drama...