LOL... how can they even ARGUE that it doesn't harm your driving abilities xD Look at Nicole Ritchie for example when she was hopped up on painkillers and weed and was driving down the wrong side of the road. That's like a drunk driver insisting that he drives better while drunk.
she was driving on the wrong side of the road because she was on painkillers. i can be high as hell and i drive like im sober.
http://abovetheignorance.org/ explains marijuana benefits and how its really not harmful at all. it also has multiple links to studies that back it up.