In many (OK, all) other industrial nations, there is bullying, homophobia, gender sterotypes, racism, their own flavors of aggrieved entitled masculinity, and other similar psycho-social factors. You agree these are not unique to the USA, but then say they are important in understanding mass shooting frequency in the USA vs. other countries. So - how are they important?

If all these factors exist in those other countries, what then makes the difference in the USA? Not just in mass shootings, but in the drastically greater level of gun violence overall in the USA, compared to all these other countries?

It's got something to do with culture, for sure.