Look, for example, at the obvious, immediate, practical example of illegal Mexican immigration. Now, that Mexican immigration, over the border, is a good thing. It's a good thing for the illegal immigrants. It's a good thing for the United States. It's a good thing for the citizens of the country. But, it's only good so long as its illegal.
It is odd enough to see how the entrance of a person of the opposite sex into an assemblage of either men or women calms down the little discordances and the disturbance of mood.