The problem with that pov is that you can apply it to anything. If police officers didn't carry guns, criminals would be less likely to die also. However, yes, I will concede the point that if Zimmerman hadn't had a gun, no one would have died. Also, if Trayvon hadn't turned around when he got home and confronted Zimmerman, no one would have died.
However, you should be willing to concede that there is a possibility Zimmerman would have received seriously bodily injury or death. This wasn't some little fight between brothers or a fight with abunch of onlookers to separate it when it got ugly.