If you carry a concealed firearm, you will invariably hear a variation of this: "Why do you need to carry a gun? A Taser is just as good, and you won't kill anyone."
Here is a story about a couple who was arrested when they attacked a security guard who had just deployed a Taser against them. After shrugging off the shock, they turned it on him and beat him senseless. The guard was foolish at best. He entered a fight that had at least 4 participants, while carrying a contact weapon (or if it fired darts, a single shot weapon with a range of only 20 feet) and got his ass handed to him.
Tasers are ineffective in a situation like that.