It sounds like you’re claiming that the US just has more criminals per capita.

There’s a reason we have so many violent gangs in the US. We don’t take care of people the way other countries do, and we take advantage of every marginalized population we can.

Except that you can't do that either because someone acting in bad faith can just say that there were other confounders, because there will always be other confounders, since we can't make a proper control group out of a society. Immigration/emigration, other policy changes on county/state/federal level, delayed effects of 30-year old policies (such as Roe vs. Wade or banning lead in gasoline), etc. There's no such thing as fair comparisons in the social sciences; we can only and have to act on imperfect information.

What has diversity got to do with anything? Australia is a country of immigrants with people for all over the world living with dramatically less crime per capital than the US. Are you claiming that certain races or cultures are somehow inherently more criminal? If yes please provide evidence.