In short both.
Handling: as a Physics teacher and former engineer, there is certainly
a safety and handling penalty for SUV's. Can't get past that. More weight makes stopping, changing direction and efficiency suffer.
Environmental: this is an area fraught with politics, subjective opinion, error and bollocks. Modern Green-hero cars such as the Prius are as environmentally destructive over their life-cycle as any SUV on average. It is manly the batteries that do this, but these are a serious flaw in the "my Prius is environmentally sound" argument.
There is a tendency towards people believing the false notion that thier big machine is safer than a well designed normal car. In small accidents, they might suffer less damage. In big accidents, they transfer energy to the occupants and what they hit. It might be all very well to say "Im alright Jack" but many people do drive with reckless abandon in SUV's.
EDIT
As for humans not being responsible for Global Warming, I tend to agree. The science is still dodgy, despite all the spin and talk by the likes of Al Gore.