If holy men suppress their sexuality for the greater good of the group, how then is everything in their behaviour motivated by sex?
Next you define being asexual as a pathology, that comes quite close to a "no true Scotsman" argument, or a circular argument. It exists, so why is it a pathology? And even if it were a pathology, it still exists as a counterexample.
I still think these examples make it a bit harder to see sex, or at least continuation of genes, as the sole and universal motivator for everyone.
It is, of course, very important, but a universal explanation for all everyone does, well, I'm unconvinced. But that doesn't matter, I wouldn't have thought about it if you had not posted this.
Holy men don't just advocate about all people. They advocate for their own group, own religion and at the core of it all is for them to grow in numbers. Also, let us not kid ourselves. "Holy men' that supposedly deny their sexuality do enjoy it, just behind close doors. Also they are often homosexuals (as it has been demonstrated many times). Even he denial of sex, and thus turning into a holy man, comes down to be about sex.
I believe at least that all healthy organisms have a healthy sexual function. This is why and how they come to exist. If one doesn't "have it" then they are most likely sick. If it is a choice (egg/chicken thing) then again, denial of sex makes one choices revolve around it. (e.g betterment of humanity).
Also, even if your speculation is correct the outliers you mention are to be expected in any species. Nothing is ever 100% is nature. That's the whole point.