The Buddha explains the power of sensual desire. The form, sound, and even taste of (in his telling) the opposite sex, or rather, those which we desire, to expand just a tad. It is funny that above all else, all the other hindrances, it is "women" -- over money, fame, power. It's a primal instinct, though. I don't think the Buddha is warning, so much as he is making an observation.