I suggest adding a cooldown to the PvP toggle for the Plaza. Either a fix one of like one minute or a more reactive one that only kicks in after you engaged into player combat and that lasts for like 5 minutes. There should also be a grace period that shows you as PvP flagged but prevents you from taking/dealing damage right after you turned it on - perhaps 5 seconds or so.
Currently people just walk up to you, toggle PvP on, kill you and then turn it back off, kinda pointless.