So blinglovin, you're accepting that the principle of utility is only 'normal' (and not universal) practice? Which simply serves to make the point that neo-classical economic theory is based on entirely theoretical grounds and not empirical ones.
In actuality, most mental health deviations are excessive versions of normal health behaviour or are not well enough understood to be able to determine their precise causality (pace schizophrenia).
You said anorexia etc were 'considered diseases' for a reason: ie that they are not 'normal'. This is absolutely right: we have medicalised what is in fact part of the 'normal' range of behaviour.
You accept then that these do constitute apparently 'irrational' non-utility serving behaviour; yet the features of mental health deviancies are present in micro versions in most of us (the chocolate you know you 'shouldn't' eat but you do anyway; the phobia that keeps you away from spiders even though you know they can't harm you; the habitual practice you can't quite shake off even though you want to). The soldier's duty is - as you say - also an outlier, but a sense of duty is not so far away from many peoples' experience, especially in cultures other than our own.
Rational homo economicus is a figment of the theorist's imagination despite how comforting an idea it is.