Of course Saddam's ruthlessness is a reason to attack. It is a reason for every human being on earth to kill him by any means available at any time available, as an act of the simplest justice.
Are there other reasons as well? Sure. That's gravy. Saddam should be removed from power because he uses power unjustly. He should be killed because he needs killing. All the rest of it is boilerplate around that fundamental, moral reality.
He goes beyond the necessary brutality required by authoritarian Middle East dictators trying to suppress internal independence movements including Islamic radicalism. That's too bad, but not surprising. Do you seriously expect anybody less than a thug to pull that off?