Every year around this time I consider getting a good handgun and renewing my concealed weapon permit. But the doctrine of preemptive war does not apply to cyclists who feel threatened by malicious or negligent drivers in huge vehicles. Replying to a close pass or an aggressive swerve with hot lead would not be considered self defense. It would only make matters worse. By the time you could be sure that deadly force was justified, it would be too late to use it.
Since armed resistance would not improve the riding environment for any cyclist, the artillery is not worth the weight and bulk. If anything it would justify a driver's more deadly actions. They could claim to have been threatened first.
After September 11, 2001, all Americans felt what it was like to fear an unprovoked deadly attack punishing them for actions they considered harmelss lifestyle choices. Bicyclists on the road have felt that for years.