"I was here first" isn't an argument for/against anything. If someone rolls in and takes your spot and you are unable to hold your ground, then the mobs are theirs. There isn't any PvP or PK in this game so either walk away or fight for your spot until someone gives up.
They could be civilized and move on if they see you there (and some will), but make no mistake, nobody is being forced to be courteous.