I agree with your evopsych explanation. Political correctness is to do with status, as noted by Kristian at http://www.iea.org.uk/blog/the-economics-of-political-correc... but even he doesn't go so far as to connect it to sexual competition. Sexual competition, especially without enforced 1-on-1 pairings (e.g.: marriage of the past), does lead to conflict. Cases like that of Elliot Rodgers come to my mind.
However I'm not convinced that enforced monogamy has seen less conflict than modern times. Can you back this argument with statistics? For example, did crime rate increase? My feeling is that even in the good old days where 1-on-1 marriage was the norm, high-status males still surreptitiously poached females paired with lower-status males. Per certain writers even the Victorian Era was not immune to it.
Pinker suggests that violence has in fact declined over time: http://en.wikipedia.org/wiki/The_Better_Angels_of_Our_Nature