Homosexuality and Heterosexuality Are Cultural Constructs

R. V. Young makes the point I was making the other day:

For thousands of years, until the late 1800s, our ancestors were completely oblivious to the existence of a fundamentally distinct class of human beings. Indeed, during the long period of Greco-Roman antiquity and more than a millennium and a half of Christian civilization, man did not even have a name for this class. 

Or so asserts an almost universal assumption fixed in the language almost everyone uses: that “heterosexuals” and “homosexuals” are two permanently and innately different kinds of human being, and that “sexual orientation” constitutes a difference comparable to the difference between male and female. Widespread acceptance of “homosexuality” and associated terms thus biases discussion of the subject before an argument is even formulated. 

What might be called the philological evidence calls this notion into question. If it were true, someone would long ago have given this class a name. That no one did until very recently suggests that the notion is not true.

The last point states what I think is a rather obvious point, and I was shocked when someone disputed it in the comments!