Legislative Immunity: Necessary Protection or Unfair Advantage?

In Arizona, repeal of a little privilege called legislative immunity has been brought up. Essentially, legislative immunity bars "the arrest of legislators during, and 15 days before, legislative sessions," with the exceptions of "treason, felony or breach of the peace."
Last year, then-Senator Scott Bundgaard was involved in a fight with his girlfriend on the side of a freeway. The fight left both of them with cuts and bruises. When police arrived and handcuffed Bundgaard, Bundgaard asserted his position as a legislator and, alluding to the constitutional provision of legislative immunity, insisted they remove his handcuffs. Bundgaard spent that night at his house, free from arrest, while his girlfriend spent that night in jail. Although his girlfriend was later deemed the victim in the case, Bundgaard would have been "arrested on possible domestic violence charges and suspicion of DUI on the night of the incident if not for the immunity law."
There have been other cases, too. A legislator in Arksansas leads officers on a "high-speed chase through two counties and doesn't get taken into custody." A Georgia lawmaker says he "couldn't be prosecuted on a DUI charge."
However, some believe reaction to legislative immunity has been too quick and impulsive. Does legislative immunity protect our legislators and help ensure their best performance in sessions or does it give them an unreasonable privilege?