If you don't see a clear difference between the hard sciences of biology/chemistry/medicine and the opinionated "science" of parenting (prescriptive, no less), then you should check your eyes.
I see your point about different qualities of science, but the wording of "highly tuned parental instincts" is still bad. The instincts are the same in both situations, and they're highly flawed. Science should override instincts in lots of situations.
And if you ask basically any kind of science "how do I best accomplish x?", that science will have a "presciptive" answer, so I don't see how parenting science is any more prescriptive then chemistry.