So, multiboxing if you control all 6 characters signally and you have to type a command for all 6 characters separately is ok. Multi-boxing with the use of hardware OR software which allows you to control 6 characters with 1 command is not ok and considered in violation of the spirit of the game as it gives the player(s) an advantage over other players.
Sounds more like the misguided, probably biased opinion of that GM. How about I have 6 individual keyboards for 6 computers running one account each. How about I make a fully mechanical device that physically presses whichever key on all 6 keyboards via one control point. Would that be ok?

Really, the spirit of the game? Sounds like the same type of person that will also go on to preach about "the journey and not the distination" to people powerleveling up their 100th character.

Boxing gives me an advantage over a single player because .....I gotz more accounts. Boxing does not give me any advantages over a group of players, in fact, my "group" is far less effective. And I don't think at any point that it gives me an "unfair" advantage. Hey.....those two guys grouped up...that means they have an "unfair" advantage over a solo player? I am playing on a computer that runs the game at all the settings maxxed and great FPS on a huge ass high res screen that makes it easy for me to see everything.......I guess that's an "unfair" advantage since there are probably people out there playing on something tht barely runs the game?

This "GM" sounds like she/he is making company policy off her/his personal opinion. Go over that person's head if you can, cause I don't think the left hand knows what the right hand is doing at SoE and if it did, that GM will probably get a quick slap to STFU and stop losing us $$$.