Flavor chemists have found that cilantro aroma is created by a half-dozen or so substances, and most of these are modified fragments of fat molecules called aldehydes. The same or similar aldehydes are also found in soaps and lotions and the bug family of insects.
The published studies of cilantro aroma describe individual aldehydes as having both cilantrolike and soapy qualities. Several flavor chemists told me in e-mail messages that they smell a soapy note in the whole herb as well, but still find its aroma fresh and pleasant.
If the flavor doesn't fit a familiar food experience, and instead fits into a pattern that involves chemical cleaning agents and dirt, or crawly insects, then the brain highlights the mismatch and the potential threat to our safety. We react strongly and throw the offending ingredient on the floor where it belongs.