Its a bad idea. Anyway, what constitutes a threat? People will start gunning down their "attackers" and killing them, and there would be no way to tell how much a threat the attacker posed. Maybe he looked at someone the wrong way, and instead of turning away they shoot him. Some people are going to use this law as an excuse to kill whoever they want. And with any gun battle that may break out between two people, some bystanders will be caught in the middle.

Even if the majority of people are responsible gun owners, a lot of people will needlessly die under this law, and as ghosttoker said most of them will be living in your household.