It’s logically consistent. Therefore, if you are in support of banning guns to stop violent crime you must also be in support of banning pencils to stop people from getting bad grades. You may have already observed this but they do not follow this course of action.
One must therefore conclude that the reason for their desire for banning guns has nothing to do with the stated goal of reducing violent crime. It must be something else such as a desire to control people.
Another alternative which has legitimate application in many cases is that anti-gun people do not confine themselves to logical thought processes. One Marxist professor I talked with even express pride of being able to break free of such constraints.