I think the etiquette depends on the type of lot/garage. At Dallas Love, there were a small number of charging spots in each of the 3 garages. B and C garages were only long-term parking, so I had no problem parking my car in one of those spots and leaving it. Garage A doubles as close long-term plus short-term/pickup. Never used this garage with an EV, and the charging spots were somewhat close to but definitely separate from the short-term spots. So tough call, I wouldn't begrudge someone using them long-term, since they are surrounded by non-charging long-term parking.
I agree that, at least at airports, what's needed really are just outlets in numerous spots. No long term parker needs anything more than trickle charge. This will just take time to become a norm among communities and planners, though it might be easy to retrofit in garages with the lighting system already in place.