I don't think I would classify this as an unrealistic expectation, because it's not really an expectation as much as a misindoctrination. The behavior is the expected part; people are generally comfortable with many philosophies as long as they lead to the desired behavior.

I think it is very important to remember that desire is a gift and a blessing from the Lord. I remember obtaining this impression as I read a book by David B. Haight as a youth, and it has a positive transformative effect on my thinking. It became okay to have impulses as long as they were circumscribed within the Lord's boundaries.

General Authorities try to make a point of this within almost all talks regarding chastity, though it's often lost in the condemnations.