Speaking as a man...

Such objectification is an inevitability of our psycho-sexual programming from which all our perceptive mechanisms ultimately derive; thus all such 'beauty' is objectified in terms of image / resonance which exists as a fundamental pattern to which we are biologically programmed (rather than culturally conditioned) to respond.

So - Nature: 1 / Nurture: 0

Once we've succesfully resolved our Oedipal Complexities, then we might gleefully indulge ourselves on whatever level might be practicable, or acceptable, in the recogition of the myriad variables on offer, but which are all just an aspect of the one resplendant principle from which, as men, we're otherwise excommunicated.

Why do men have nipples? Vestigial reminders of what might have been; likewise that tell-tale line of closure on our scrotums that places us into the realm of the masculine & therefore the merely servile! Given that the dynamic morphology of the penis is determined solely for the pleasure of the vagina (though not without rewards), it's interesting that Sigmund could come up with something as laugable as Penis Envy; one would have thought Breast Envy would be a far more likely condition.

All very heterosexual I know, but where we score is to take such psycho-sexual subroutines (which only exist to coerce us into procreation) & use them for the pure joy of it. Next time someone says Gay Sex ain't natural, then point at a train, which don't exactly grow on trees - but they still work perfectly!

Final score: Nature: 1 / Nurture: 23 - no contest!

One thing I'll ever get though: Breast Implants - nature wins out there each & every time.