The problem here isn't that "sexual selection" isn't a useful concept on its own; the problem is the failure to appreciate how abstract the concept of "natural selection" is.

I think there's a substantive dispute here, not merely semantics. The original complaint was that Natural Selection was an unconstrained theory; the point of my comment was that in specific cases, the actual operating selective mechanisms obey specific constraints. The more abstract a concept is (in OO terms, the higher in the class hierarchy), the less constraints it obeys. Saying that natural selection is an abstract concept that encompasses a variety of specific mechanisms is all well and good, but you can't instantiate an abstract class.