Indeed, unless the society is somehow totalitarian, there are bound to be conflicting social trends, some favouring extroverts, for instance, and others favouring introverts. As I argue at length elsewhere, Christianity is internally conflicted between the Jesus cult of niceness, and the mainstream, politicized culture of Christendom.

That's a good point about how nice guys might have a silver lining in not being considered competitors. So niceness might have evolutionary value as a kind of cloaking device.