True, but such a person would be aware of the lack of mixed messages, and if they find themselves unable not to interpret the friendship privileges as such and not as leading them on, they could back off/pull away a little so as to prevent their feelings being hurt. Or they could simply say that they see the privileges that way, and that it hurts. Although people tend to be emotionally masochistic up to a point, so I don't know how well that would work.

I don't know that giving friendship privileges to someone who's interested is automatically leading them on; it could just be continuing the friendship, and not treating the interested person differently. It seems like the only alternative in that situation is a less close friendship, and I think that might be worse (again with the emotional masochism though).