"Disabled stalls" are there for those that need them, but there's no reason to insist that others don't use them if there's not a disabled person right there right then that needs it. I vastly prefer disabled stalls for the "elbow room". It's rather annoying to be smacking your elbows into both partitions trying to get at or use the TP, or when trying to pull back up your pants etc. Some bathrooms clearly have more stalls in them with less user-space than common-sense would seem to suggest. (there may be a building code that covers non-disabled stall size, I don't know)
Maybe a complainer may be comparing them to something like a disabled parking space. THOSE are much more prone to abuse because of the larger number of users, and the much longer duration of use. So for them we have to put up fines to discourage the inconsiderate people that take up a very limited resource for an extended period of time.
Though over in europe they've got those special keyed toilets, I guess they have more of a problem over there somehow? Anyone have some more first-hand knowledge/experience/insight on why they have keys over there? I've never seen a problem here in the USA and we don't need to lock them?