It isn't that reductive reasoning is dangerous in itself - so long as the one doing the reducing keeps in mind what is being reduced from - but that the artifacts it generates become these sorts of fetish objects which authoritarians can use to fix rigid frameworks.
So someone says, "well so and so is doing this because of biological drives." Ok so the biological drives have been "sliced" out of the multiplicity of causation to illustrate a certain point, to make comprehensible the infinitely complex and incomprehensible real. Great. It is a story, and we can use this sometimes.
It is when you have someone saying, "But it is biology. We can't mess with it. End of story." And then they point to this mysterious "biology" as if reality can't possibly proceed past its bounds, and that upon following the instructions that biology conjures up with its galaxy of related symbols - which also have to be constructed - then some god of explanation is satisfied.
