Not the GP, but my personal impression is that US culture glorifies violence and conflict, as conflict, rather than co-operation, is seen as a way to get ahead on an individual level. That spreads through all layers of society including law enforcement.

It is obviously not something that can be blamed on any specific individual, and it's only based on what things looks like from the outside, but the impression is there regardless.

The ridiculous amount of wars the US wages upon other countries also contribute to that image, but I suspect that's more related to the US fighting seemingly neo-colonial wars with European support than anything else. If European contribution had been on the same level, that factor would probably not be included.