Well, if they use your approach, their arguments CAN be dismissed. You take one small slice of criminal statistics, rape/domestic assault, and compare it to all firearms related deaths. The only reasonable comparison is between all firearm related deaths and all defensive uses of firearms. Serious studies, such as John Lott's "More Guns, Less Crime," show that guns are used for defense over two million times each year. Simply showing a gun is sufficient to send most criminals scurrying for easier prey.
See how easily their arguments can be dismissed?