What do people argue about

Assume we have two persons. All fine. They may have some topics to talk in common and then they'll be friends or at least will get along quite well (if one of them doesn't behave extremely bad in some aspect, but this is rare). If they don't have the topics in common, they won't talk one to each other too often. But by and large they won't get in arguments too often (except sometimes if they are in very close relationships - roommates, partners, family members and yes, also good friends - and this is because of how much they depend one on each other, and usually not because of some animosity).
Yet there are topics about which a lot of people argue, no matter if they're close friends, or total strangers. They may be in accord in all the important topics (style of life, personal ethics...). Yet here begin problems. It's when they talk about how to best rule to the other people (i.e. politics). Weird, isn't it?