I will cough up my passphrase at the mere *suggestion* of torture. I would probably give up my passphrase if a scary person were to just ask nicely for it.
If Qubes were to incorporate any deniability features, I (and anybody who dislikes being tortured) would require a means to show absolutely that such features were not enabled. These are dangerous features because the moment they are incorporated we would all be using them, whether we are or not.