"Why do you need an AR15?"

[stanc]

One doesn’t “need” a defensive weapon until he desperately needs one.

Indeed. However, assault rifles are offensive weapons. And one is unlikely to have an assault rifle on one's person when desperately needed.
Handguns are defensive weapons. They are practical for continuous carry on one's person, for immediate access when desperately needed.

It is also the reason we need to aggressively resist and work to roll back restrictions on weapon ownership regardless of whether the weon os a firearm, knife, baseball bat, etc.

Never gonna happen. Even most pro-2A folks think there should be reasonable restrictions.
Only difference between them and the anti-gun crowd is in what they consider "reasonable."