5-year-old shoots his 2-year-old sister

But the difference is, person X generally knows how to operate the gun; a 2 year old child doesn't.

The point Joe was trying to make is that in more situations than you'd think, the law-abiding citizen who owns a gun wouldn't be able to defend themselves either. Much like a two-year-old. If the 5-year-old had shot his mother, who undoubtedly knows how to handle guns, would she have been able to do anything about it?

Obviously, sarcasm works much better if you agree with its message, not so much if you don't.