I'm not sure whether I agree that all people intrinsically seek out conflict. Yes, from a natural selection standpoint, as brought up above, humans have had to compete for natural resources our entire existence. And undoubtedly there are personalities of people who instigate conflict, both on a small and large scale. But we should also take into account the number of people who prefer to avoid conflict. The entire ideology of pacifism is based on avoiding conflict, for example.
I believe the matter is separated by personality type rather than being a basic human instinct. Yes, some conflict is unavoidable, but again, I think it's hard to prove that every one of us seeks out disputes. If that was not the case, there would be no existence of religious, political, or racial tolerance in the world. The embracement or rejection of conflict is rather something that is idiosyncratic to each particular individual.
That said, it is probably worth considering the fact that advancements in our societies have awarded us the luxury of being able to avoid conflict without sacrificing the ability to be successful in our environment. Perhaps only extremely dominant and aggressive individuals long ago would have found success. Today, however, with less threat to survival and more open access to natural resources for all, there is room in society for those who would rather not have to seek out disputes.