Should a state senator have immunity from a domestic violence charge?

An Arizona state senator involved in a domestic dispute last weekend cannot be charged because Arizona law states legislators are immune from arrest “in all cases except treason, felony, and breach of the peace” while the legislator is in session.
Senator Scott Bungaard and his girlfriend, Aubry Ballard, got into a fight while driving home from a charity event last weekend.
Ballard accused the senator of inappropriately touching a woman he had danced with that evening.  A fight between the pair ensued and he said she started punching him and throwing his things out of the moving vehicle.
Phoenix police officers that responded to the scene said both Ballard and Bungaard sustained marks indicating a domestic dispute.
Ballard was arrested on suspicion of misdemeanor assault and taken to jail.  Bungaard was not arrested and he told the police he was immune from arrest.  Authorities say he could be charged at a later date.
Should a senator be immune from prosecution during a legislative session?