"Assume everyone can potentially be either, and doll out rights and protections accordingly."
It is a good thing the founders of the United States saw rights as pre-existing and not something to dole out based on the understanding that people can potentially be victims or criminals.
"It's a fallacy to believe that criminals can never be victims, and victims can never be criminals."
I am not certain anyone is suggesting that. I will suggest, however, that the vast majority of lawful gun owners do not turn into victimizers. How many legal, privately owned firearms are in the United States? 100 million? 200 million? How many of those legally owned firearms are used in crimes?
Granted, we have an appalling level of violence in this country, and much is perpetrated with firearms. But of that gun violence, the majority is considered criminal-on-criminal, using illegally obtained firearms.