It has become unfashionable in some circles these days to note the differences between men and women, to suggest that such differences are more than social constructs--and therefore, perfectly acceptable to note!
After all, we humans note many differences throughout the natural world--to our endless delight: the differences between summer and fall, the differences over time as leaves in Northeastern North America change, the differences created by the first snowfall. We note differences in appearance, in personality, not just between humans but between our pets. Naturalists naturally note differences within animal species, including the male and female of the species.For that matter, a doctor who indifferently failed to note the differences between male and female patients would be lazy at best and sueable at worst.
And yet there's a push to downplay these differences for a variety of reasons. One reason: differences so easily move from observation to judgment, extending outward to include behaviors that have nothing to do with biology at all. It is also very easy for these judgments to move backwards--this is how one ought to behave. 
So the observation Women give birth becomes Women are better with children becomes Women are emotional and subjective (like children), not intellectual becomes All women are extroverted cheerleaders who like solving family problems which becomes If this is your label, you should consider nursing, not firefighting.
Or the observation Men are stronger than women becomes Men are better at protection becomes Men are tough and unfeeling becomes All men are gruff weight-lifters who fight rather than talk which becomes If this is your label, you should be watching action films and considering a career in business, not teaching.There's nothing wrong with being a cheerleader. Or a gruff weight-lifter. There's nothing wrong with going into nursing. Or business. Or fire-fighting. Or teaching. But the assumptions can become irritating and flattening.
However, differences between women and men at the biological level do have ramifications at the behavioral level. In a free society, more women do in fact choose to go into teaching and nursing, that is, people-oriented professions.Like with genetics, so many factors come into play, I argue that it is best--in the day-to-day--for people to treat each other as individuals.
That doesn't change the inherent fascination that men and women have for each other, in all their variations. I would argue that the "cliched" male interest in lesbians is a fascination with women pushed one extra step: If one woman is interesting, why not two? And I would argue that the sometimes derided female interest in gays is the same: If one man is interesting, why not two?
There is a sexual component here. But it likely originates in something even more basic. After all, the male and female of a species are stuck together on a single planet: one figuring out the other is part of survival.
The great thing about M/M romances is that unlike mainstream M/F romances--which tend to use Darcys and Thors with the occasional Loki thrown in for fun--the males in M/M run a full range of possible male protagonists from slender effeminate cutie-pies to brash sports heroes, from wily politicians to skeptical and exhausted advisors (see panel), from close-mouthed business owners to geeky adorkable computer guys, from sarcastic artists and inventors to heroic and/or traumatized military men.That is, the best M/M romances (and yaoi) explore the male of the species whilst supplying variation within that biological reality.
And the more you read, the more variation you get!
