You can speculate on the root cause of murder, but simple demographic data explains the different numbers between the US and other developed countries.
The fact is that everywhere, homicide rates differ dramatically by age, gender, race and ethnicity. Some countries show bigger variation than the US does.
If you control for those variables, the difference mostly goes away.
e.g. compare data for whites of the same age and gender to Western Europe, US Hispanics to Latin America, or African Americans to Africans, and the US data does not look so different.
I don't see why this fact should give rise to cries of racism, when it is just as much sexist and ageist.