63% Americans identified as Christians (2020 Pew Study). That number has been declining for decades (75% in 2015, 70.6% in 2014, 78% in 2012, 81.6% in 2001, and 85% in 1990).
29% of Americans identified as unaffiliated, atheist, or agnostic.
Meanwhile, violent crime in the United States has also been on a sharp decline during those exact periods.
The lowest crime rates in the world are Switzerland, Denmark, Norway, and Japan (the latter 3 have some of the most restrictive gun laws in the world).
Switzerland is 29% unaffiliated and 62% Christian. Denmark is 74% Christian (only 4% regularly attend church, and only 19% said religion was an important part of life). I could not find good data on their unaffiliated. Norway is 18% unaffiliated and 71% Christian. Japan is 62% irreligion and 1% Christian (obviously Christianity would be an outlier here).
Christianity is on the decline in all of those countries while unaffiliated is on the rise. All those countries list at the top of the most happiest and healthiest countries in the world.
Venezuela, Papua New Guinea, and South Africa have the highest crime rates in the world.
Venezuela has the highest crime rate with 89% of it's population as Christian and 8% no religion.
Papua New Guinea is 96% Christian.
South Africa is 84% Christian and 10% irreligion.
It would seem that the safest and healthiest countries have lower Christian populations, that are also on the decline. With unaffiliated being on the rise.
