but if you really want the logic stream, here it is:
- we have a background check system (NICS) which covers guns bought at federally licensed dealers
- federally licensed dealers only sell about 60% of the guns in circulation
- with 40% of guns sold in untraceable transactions, criminals buy the majority of their weapons from private sales.
- since a background check on all sales would catch whether or not a criminal is buying a gun, we should extend the current system to cover all gun sales.
but if your policy says that it's better to arm criminals rather than risk having to fill out paperwork i suppose you won't be able to follow why logic dictates that there should be no exception to background checks on all guns sold.
as for evidence, here is the closest thing i can come up with which you won't dismiss out of hand for being from a "liberal" group. i'm assuming you have nothing against johns hopkins university: http://www.jhsph.edu/research/centers-and-institutes/johns-hopkins-center-for-gun-policy-and-research/publications/WhitePaper102512_CGPR.pdf
"That's the trouble with political jokes in this country... they get elected!" -- Dave Lippman