No, I think it works just fine. If I own a gun, and suddenly they become outlawed, I too become an outlaw.
That has never been what the phrase meant. It has always meant that if you outlaw something, then it won't stop the outlaws from having it, because by virtue of being outlaws they'll ignore the law anyway.
In the case of guns specifically it amounts to effectively disarming the law abiding citizens, leaving only the criminals with guns.
It has never meant that if you outlaw something that suddenly all the law abiding citizens will be outlaws too.
The point is, if you ban something that is commonly used or owned, people will suddenly become outlaws for no other reason than because it illegal to have.
There is, of course, some truth to that too, but it is not the point the maxim makes. Law abiding people presumably will abide by the law and dispose of the contraband in an orderly fashion.
For example, If your neighbors all commonly dumped old/extra pesticides, gasoline, motor oil, etc into the river, and a law banning the dumping of such into the river was passed, I expect they are generally law abiding, and they would stop. It wouldn't suddenly criminalize all of them.