From a purely evolutionary perspective, murder was and is never as adaptive as ethnocentrism.

The high cost of the former act can only be justified, in a purely economic sense, if the reward for doing so outweighs the risk AND repercussions of getting caught. And in most parts of the modern world, where law and order is strong, murder for personal gain is thus rarely ever beneficial, to both the perpetrator and to his/her community, and so is rightfully condemned.

Ethnocentrism on the other hand provided tremendous survival value to our species in the past, and continues to do so by granting a group some abstract concept to bond over, even though it is not abstract since ethnocentrism is literally favoring your extended family, thus facilitating in-group cooperation. As a result of this, ethnocentric groups have been more successful than non-ethnocentric ones.

So yes, while murder and clannishness are both part of human nature, they do not manifest as behavioral traits to nearly the same degree. And there's definitely enough quantitative difference in their respective prevalence to make a qualitative difference in the way they should be perceived, judged and implemented.