Honestly, if this attack should teach us anything, it is how dangerous an infinitely defended individual is. Without body armor, this man could have been stopped with any CCW, but was nearly invincible with his equipment, and unassailable from his position in the corner of the theatre. It doesn't matter how "effective" the attacker is, if no one can stop him. BTW, this killer had to dump the rifle when it jammed on him (and he probably only brought one mag because it was so big).
Correct me if I'm incorrect in my interpretation (with facts/precedent, please) as I'm not a "Constitutional Scholar":
We have a right to bear arms, but not armor (that is an important distinction, in my mind.) Our fore-fathers wanted for us to have the right to engage a tyranical government in battle as a last resort, but I cannot believe they upheld the right of one man to tyranize his fellow citizens through tactical advantage. So long as an aggressor is vulnerable, he can always be stopped. But with a sufficiently strong defense, he has true impunity, and is above governance. Which is why this crime is so particularly horrifying to us gun owners. This was a situation in which we could do absolutely nothing other than shield those around us.