An interesting hypothesis, but if true I would expect to see a greater effect in cities than in rural areas. What I actually see is, if anything, the reverse.
There's a reason why people think of cities as crime pits. It's because most they grew up in a world in which that was accurate. Just picking one city as an example although it looks about like this for most/all of them:
https://en.wikipedia.org/wiki/File:NYC_murders2.png
The years across the bottom of that example are the years in which the NYC murders
happened. If you adjust them all down a couple of decades or a bit more, you get roughly when the people who committed those crimes were
born or were still young
children. And then it fits pretty well with how much lead there was in the air for those years. So the crimes happened right when the most leaded-up generations of people hit peak crime ages, and went down when their lower-lead successors reached the same ages. One might then wonder what kind of behavior these generations would then get up to once they were well past peak crime age; I'll get back to that later.
In general, rural crime information is harder to find separately from urban crime information, because it doesn't get as much attention, because crime also generally scales with population density, and because rural subcultures pride themselves on their image of low crime and are thus less likely to collect & publish the data. Searching for crime rate trends with time and the word "rural" didn't yield anything, nor did replacing "rural" with "Wyoming" or "Montana". But I did find this example from Nebraska, showing crime going up & down at about the same times as in NYC:
https://www.americashealthrankings....easure/110/state/NE/facebook/size/600x300.jpg
In addition to the Nebraska example, here's one from the FBI which includes not only cities or a particular state but the whole country, which is about half-&-half rural/urban by population, and in this case they even explicitly included the time-adjusted lead graph as I suggested with the one from NYC above:
http://www.cambridgeblog.org/crime-vs-pb22-yrs/
So it looks about the same; including rural areas along with the cities doesn't dampen the effect of change with time. Rural crime rates might be lower at any given time than urban, but they move up & down in parallel over time. When one goes up, they both do, and when one goes down, they both do, regardless of which one is consistently lower or higher.
That actually fits what would be expected from environmental lead distribution; it's not particularly concentrated in cities but all over everywhere. How high the level was getting was first discovered by geologists & physicists trying to use element & isotope ratios to find the ages of rocks way out in deserts and seeing how far the abundance of lead on everything kept throwing off their results. It might have been getting released mostly in cities, but it blew around easily.
In fact, the lead signal in the data is so strong, and rural crime information on its own is so much less published than urban or combined information, that an image search for rural crime trends in the 20th century, without the word "lead" in the search at all, scooped up a bunch of results that weren't specific to rural locations and brought lead into the picture anyway... like these, where we can see that (taken whole countries at a time so urban & rural are both included) the same thing happened not only in the USA but also in Canada, Australia, the UK, and New Zealand, most of the last of which is globally about as far away from most major cities as you can get on land:
https://www.motherjones.com/wp-cont...g_lead_crime_international.jpg?resize=990,610
So, what would crime data and lead being pretty thoroughly distributed everywhere regardless of the urban/rural distinction have to do with political/economic/philosophical positions that are unempathetic/hostile but aren't crimes and seem more common in rural areas? Well, crime is just one symptom or set of symptoms of anti-social behavior (or the associated disorder), and lead is medically known to increase not just that one but the rest too.
Other aspects of antisocial behavior include, as Wikipedia puts it, "actions that harm or lack consideration for the well-being of others... any type of conduct that violates the basic rights of another person and any behaviour that is considered to be disruptive to others... covert and overt hostility". Arguing for policies that harm people certainly fits that, especially when the argument boils down to simply a complaint that the alternative would be too beneficial and help too much.
And the circumstances in which that's what we get just happen to be circumstances in which antisocial tendencies are known to be increased (such as unnaturally high lead levels) but crime is known to be decreased for unrelated reasons (such as being older than typical criminal age range and/or living in a low-population-density area where one is less often around many strangers). In other words, it's just what would be predicted by a theory that, when antisocial tendencies would be present but don't take the form of crimes, they take other forms instead, such as support of policies & philosophies that just financially/emotionally/culturally harm people for the sake of harming people. The generations that did the most crime when they were at peak criminal age got older and are now at the age of peak economic & political power & control. And what's changed about them is not whether they behave destructively to other people but just what form their destructiveness to other people takes. As Biden said it himself when asked about the fact that the problems facing young adults now are factually, objectively, mathematically much greater than they were for his generation, "Gimme a break! I have no empathy!". Meanwhile, the same principle applies geographically as well as chronologically: in low-crime locations, those who would do something antisocial are less likely to commit crime but more likely to favor hostile/hateful/judgemental philosophies and their resulting policies.
