I think we managed to live without national gun laws up until 1934. I don't see that the gun laws have prevented anything except to limit law abiding citizens. Teenage gang members seem to find guns pretty easily even though they are prohibited.
Reading and viewing some of the stories of gangsters back in the 1920s and 1930s BEFORE the NFA, it seems they preferred to steal BARs and tommy guns from police and NG armories rather than purchasing them.
Same as sex offenders, if someone is too dangerous to live in society as a free citizen, then why are they out?
I agree that given the current law, if a toy lower receiver can be readily used as a receiver for a centerfire upper then it should be considered a firearm. BUT, I don't trust that the BATFE is accurately representing how easily this toy does this.
I don't trust an agency that would adamantly standby their decision to label a receiver jerry rigged with string and rubber bands a machine gun. Are they coming after my doug fir 2x4s next because they could be "easily modified" into a configuration that could act as a receiver?