“you’re brain dead, you’ve got aalmost as much lead as a motherfuckin bullet in ya head.”
I doubt it’s the main cause, widespread cultural phenomena are normally mostly generated by social interactions (words) and reinforcement, and demagogues (or so they often over-claim).
Poison like that will impact a fairly small proportion and takes a long time to impact and spread. Seems unlikey to be anything major. Besides which many more sources of lead poisoning from paint and leaded petrol, and water pipes and stuff - not specifiic to US and not specific to guns.
Soul sole