You're right

If ALL guns were banned ... then they wouldn't be available to anyone. In that case, bows and arrows and slingshots might suffice.

But as long as you have a military (supported by industry) with vast arsenals of explosive weapons ... there are PLENTY of weapons available to get into the hands of criminals in the black market.

A good question to ask one's self is ...

What's the difference between soldiers and police having weapons and citizens having weapons? Are the police and military somehow magically more capable of being responsible with guns than a regular citizen ... seeing as how military and police personnel are made up of regular citizens?

-Vince