Well.. on the flip side... if you know your target is armed and you are intent on doing them harm... common sense would dictate you don't approach unless you yourself are armed, make use of tactical advantage (aka... be sneaky about it)... and pop 'em in the noggin when they least expect it.Playing devil's lettuce here, that single mother/other young women may benefit from their gun ownership being public knowledge. A knowingly armed target may well look less attractive to assault. Kind of like how poisonous animals are sometimes brightly colored.
Whereas, if you were unaware of the danger your target presents, you're more likely to find yourself at a disadvantage.
I side with the intended victim on this one. "Appear weak when you are strong..." ~Sun Tzu
The nutshell: A registry has the potential to escalate a confrontation and defeat a victims potential tactical advantage, IMHO.