Because if you do, if you accept the reality of evolution, genetics, the slow accretion of complexity through purely random changes, some of which are positive, etc., then EITHER you implicitly accept reductionism OR you must explicitly state how it is we are not just chemistry.
We are piles of complex chemistry, and not much more. In fact, nothing more, according to our best reproducible, documentable, shareable, practical, implementable knowledge. (As opposed to slippery mystical knowledge which is hard to reproduce, document, share, do anything practical with, etc.)
Yes we are piles of chemistry. "Not much more" is an empiricist conceit, as is reproducibility. But thanks for making the chauvinism of empiricist epistemology clear via your comment. You are exactly who I am complaining about, the asshole who sees people in love and thinks, "hmm, oxytocin."
Seriously, not bothered in the least. Just curious why someone would question empiricism, reductionism, etc., given how successful they have been for us in so many areas.
Especially on a site like HN, when hacking is ultimately about curiosity and discovery - and those tools, empiricism, reductionism, analysis, synthesis, etc., the whole modern package of modern science, are the best tools we have for discovery, for satisfaction of curiosity.
They're not perfect, but they are far better than many alternatives folks espouse (mysticism, anti-rationality, etc.).
Can we explain everything? Of course not! Not yet, anyway. Are there any reasons in principle why we will not be able to, eventually?
Hmm, well, if there are, we will discover those reasons using those same tools of investigation and exploration, e.g., there may be things that we determine we can never explain for reasons of computational complexity - it's just impossible to get there from here, or for reasons of incompleteness, etc.
For the record, when I see in people in love I think "Hey, that's wonderful, the world needs more of that, that's fantastic". I rarely think of the chemistry involved because it is irrelevant to that context.
But it is there (and would be entirely relevant were I studying the mechanisms involved, was I interested in the neuropsychology, etc.).
To deny its presence, though, to argue otherwise, is either to be mystical or irrational.
Or in your case, angry. And rude.
Ta!