I don't perceive Victoria as a "good" character. During her quest for revenge, she became completely and utterly evil. The Cullen family had no intention of killing James until he started to endanger their well-being by targeting Bella in some twisted game, despite his knowledge about her relationship with the Cullens. If anything, the Cullen family was acting in their defense, since James was preparing to destroy Bella. They didn't kill off Victoria's mate for the hell of it.
Victoria did drag others into her "mission" against the Cullens, including the innocent humans that she infected in Seattle to assemble an army of newborns. I have no sympathy for her after that. She was driven by heated emotions, and took it way too far. She became blinded by rage, despite the fact that the Cullens - particularly Carlisle - didn't relish the thought of killing another vampire. However, they had a cause after James cornered Bella and tried to slaughter her.
They acted out of necessity, not some twisted desire to enthusiastically play along with James and his sadistic game. I know that vampires form a close bond to their mate, but James was a fairly unsympathetic character who struck me as quite warped and despicable. If anything, Victoria was embracing hypocrisy by claiming sadness over the death of James (despite the fact that he started the entire chase) while attempting to do the very thing that she supposedly detested. They were both self-centered and unforgivably bloodthirsty.
They should have left the area after realizing that Bella was with the Cullens. James knew the risks involved with starting a battle with another coven, despite the fact that they never provoked him beyond protecting Bella after he threatened her safety. James was sick and quite fond of tormenting others by nature, as evidenced by his little "game" of chasing Bella and toying around with her. He fully deserved his fate.