Carmack does not need defending to be honest. The guy is gaming royalty - Doom and Quake alone cement his place in gaming history to be honest I don't think the new / younger generation of gamers realise quite how huge those games were when they came out.
Playing Doom 2 in multiplayer at school is probably one of my fondest gaming memories - to go to that, after only playing on consoles, was a revelation.
More clarification than anything else, I think people tend to lay all of Quake/Doom at his feet when really Carmack is and always has been about the tech rather than the game.
I just find it amusing how he managed to make such a big impact in the direction of graphics hardware and APIs yet again despite RAGE being a complete flop.