That would be a fair comparison if your brother looking at porn killed himself or another person through the action of looking at porn.  But since I'm not looking at a handgun ban, it's still not a fair comparison.  Your brother would need to kill a lot of people in a short time by looking at porn.  Not sure how he does that, but it would have to be a normal outcome of looking at porn in a certain way.  Because AR's are made for killing, that is their purpose.  I understand your point, but when we are talking about a machine made for killing lots of people, the examples start to fall through.  I understand the right to bear arms, which is why I won't touch handguns, or even semi-auto handguns, as long as the keep their mag size relatively small; but it is something we should try and prevent.  Kids shouldn't be able to by that amount of power to immediately abuse on whoever they wish.