> War-like cultures would still exist even if the Federation believes they themselves have moved beyond that type of thing.

An alternate take compatible with patio11's irreverent theory: war-like cultures exist only in the sense that some cultures have different LARP preferences.

Supporting evidence: how did the Klingon Empire (who are not actually part of the Federation) make it through their nuclear age without blowing up their planet? How do they continue to keep pace technologically with other species? They steal a lot of technology, e.g. they never invented the warp drive themselves, but that would only get them so far and wouldn't keep them competitive with the Federation.

Patio11's oddball theory of Star Trek as a documentary about a future LARP may not be correct, but it explains away these kinds of questions better than any "real" theory that I've seen!