An example: you take a girl back to your place from a nightclub. She'll say something like "we're not going to have sex" or "I'm just coming in for a coffee". If you respond honestly "actually I do want to have sex with you", she won't come back with you.

Not because you're being honest, but because you're being tactless. Compare with this answer: "oh, darn, here I was thinking you were trying to get me alone so you could have your way with me...." and that's just the first thing that popped into my head when I saw your comment. (Probably because I have a vague recollection of having said something similar to a girl once, a few minutes before she literally attacked me.)

ASD is a social calibration ping: she wants to make sure you're a cool guy. It is not necessary to lie or even conceal the truth in order to be a cool guy, it is only necessary to communicate that you understand the rules of the game being played and are willing to play it. A response like the one I gave above would be an honest answer, but not a tactless one.