I think this argument gets muddled because when you're talking about innate biology, you can either mean the overall biology of humans as a species, or the innate biology of individuals.
For example: As a species, humans are very sexual creatures. (We are MUCH more sexual than most other primates). This is basically a true statement.
But: to say that all humans are innately sexual is flat-out wrong. Individual humans have a whole range of sexual-ness, from super-sexual to asexual. And each individual human's sexuality/asexuality may be innate, something they were just born with.
So I think a lot of people get upset at the generalization about humans as a species because individual humans have such a range and variety of "innateness."
Personally, I find it useful and interesting to talk about humans as a species, but a lot of people don't.
Single, straight, female, solo, non-monogamous.