This is a very good response and looks at this whole issue from the opposite angle (instead of the typical response of dismissing it as mental illness). I suppose I never really considered that a lot of the extreme cases of female and male bodybuilders probably have the mindset of "I don't care". This is different from instances of delusion. I think a lot of these people know that they are not normal, at least appearance wise, but they may be okay with that and in fact thrive on it.
I do think however that such a drive and determination needs to be balanced by the very real physical health effects of such an extreme lifestyle. You referenced Arnold as an outlier in terms how he deviated from the norm and was prepared to go to great lengths to achieve his goal, yet he never pushed his physical and mental welfare to the extremes that many of the current bodybuilders do.
I think Arnold would do whatever it took to succeed in whatever he wanted. He didn't go to the extreme that they do now because it just wasn't necessary. With the exception of Olivia, there just wasn't anyone at the time that matched him in so far as genetic gifts. When you look at him at 21 he was already world class. Sergio was the only one at the time that was genetically superior to Arnold but he never had the discipline to get into the condition that Arnold did. Arnold also had other attributes that guaranteed his success beyond just his physique. His charisma and ability to take control of the sport so that the political climate was always on his side. Even if Sergio had the ability and drive to at least match Arnold's conditioning he was pretty much black balled from the IFBB and pretty much a non issue as far as Arnold was concern. Arnold reached a point where all he had to do was pretty much just show up and victory was assured. Arnold even said as much when he said in PI that even if Louie came in a little bit better than him, he would "put us in a room" and there he would destroy Louie mentally. Maybe so, but even if Louie was a little bit better it would have made no difference given the political climate at the time.
And Arnold proved that in 1980 when he wasn't in his best shape. His influence even carried over to the next year when his Sardinian Side Kick won with a gimp leg and glaring gyno marking the biggest travesty ever, even to this day, in the Olympia history.