When is a belief system a Mental Disorder?

Yes Scraf, it is common for people to infer conscious decision-making from discussions of adaptive behaviors. It is important to remember that organisms expressing particular behaviors need have no conscious appreciation for their choices - they are behaving in a particular way more often than in alternative ways because individuals expressing these behaviors in a similar context have left more offspring than those behaving differently. Conscious choice never enters into it. (This comment more for RR than for you).For example, females of some stalk-borers I study always lay their eggs in the plants with the fattest stalks available. They respond to stalk girth as a stimulus, but they don't KNOW that choosing fat stalks will make their offspring bigger. However, I know that because I weigh larva every year and measure plants. Females responding to this particular stimulus have been successful leaving progeny, so the response has been selected in females over time. It's much the same with lots of human behaviors, but you are never going to be conscious of *why* you respond in a certain way to a particular stimulus. And that does NOT imply determinism of behavior or lack of free will either.But to return to the question posited by the OP, I would say that a belief system becomes mental illness whenever it prevents you from acknowledging facts, causes you to deny the obviously true, or causes your consciousness to become significantly displaced from tangible reality. So basically all forms of religious mythology are capable of producing mental illness in their most ardent and extremist followers. Hence the suicide bombers.

Yes, Desmond Morris has written quite a bit about the monkey-human shift in traits signally sexual attractiveness. It also has much do with 'frontal' signaling as opposed to 'rear end' signalling accompanying the change in position of sex to a face-to-face orientation. It bears noting that what remains consistent is the clear association of sexual attractiveness traits with features directly indicative of female reproductive fertility.Human males still find all the following female features attractive.1. body shape (related to actual child-bearing ability).
2. breasts (related to child-nurturing ability, even if representing tranposed buttocks).
3. hair and skin textures and coloration (signals of overal health).
4. general indicators of youthfulness (directly correlated with potential future reproductive effort.These correlations have a lot to do with why we find these features attractive, but we don't *decide* to find them attractive because of the correlations. Rather, the correlations of these features with actual female fitness over thousands of generation have caused preferences for these features to become relatively fixed tendencies in the human population. No conscious decisions are required - we just 'feel' that way.