If that’s what is wanted, wouldn’t it make sense that effacing a serial number should be declared a crime only in conjunction with some illegal act being performed with the gun (such as a murder or robbery). We don’t want the 2nd Amendment’s purpose to be effectively nullified by proliferating paperwork type crimes.
I keep and bear arms...all of which have serial numbers. In what sense, then, does requiring serial numbers infringe on “the right of the people to keep and bear Arms”?
And Congress does have the right to regulate commerce between states. Some states have considered (passed?) laws affecting handguns made and sold in one state...although the ease with which they could be sold out of state might still put it under Congress’s Constitutional authority.