Well, I didn't read the argument like that. More like that the homicide rates are a legacy of the process of colonization; in a country that was first colonies and then a nation expanding across the North American continent, sometimes meeting hostile original inhabitants who were mercilessly and violently overrun, there was violence, and that violence necessitated self-defence, which in turn means the people traditionally rely on guns they use themselves, not the authorities and legal process - because the authorities weren't there.

Plus that in Europe, the powers-that-be have largely wanted to avoid revolutions, which means that the public's access to firearms as well as right to self-defence is restricted and police, gendarmerie and similar organisations have true monopoly on (lawful) violence. America, in turn, is a child of revolution and is revering the overthrowing of powers-that-be who were perceived as tyrants.

That's just my understanding of the history how the United States has come to this situation, not a value statement that it's how things should be.

(Just for comparison, compare to other countries colonized at the same time or earlier, like Brazil, Mexico, Argentina, Venezuela, Honduras, Colombia, Nicaragua - they all have much higher homicide rates than the U.S.)