Not saying that the NSA is innocent as a child, but please don't put all on them.
If I would have a zero-day I wouldn't go out and encrypt people computers.
But if you find a cooler with a vial of Ebola on the street, take it home instead of turning it in, then have it stolen and have that strain implicated in an outbreak?
Yeah... that's definitely at least partly on your hands.
The 'arms' in 'right to bear arms' is not clearly defined, and the founders would not have had any concept of software or weaponised software, but I can't think of an argument against people owning malicious software if the argument for owning firearms is also in play.
It shouldn't be a surprise when someone else starts shooting off doorknobs.
I would say this is closer to having your guns stolen from your home while you're asleep and then used in a crime.