As far as I'm concerned, there are no excuses for it. It was too much down on one day.Everyone needs to strive to improve. Or else how would we have Progress?
The situation described does suck, no question, but there is a limit to what Disney can constrain.
Disney's not capable of bolting guests to the ride vehicle [that is a different type of safety issue] to keep them from leaving the vehicle.
Out of curiosity, does anyone know what the issues Haunted Mansion was having? OP just said it was having issues, but was it actually down?
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Reason I ask, is I could see someone seeing the ride coming to a fullstop to facilitate a wheelchair transition as having issues, especially after everything going boom on them.
They don't need to strive to improve. They need to accomplish it.