Odbarc said:
Sexualized by society, yes.
But in terms of reproductive necessity, they're about as sexually as a beard. Not required, but they're there.
And realistically, they're bag's of fat with a nipple on them.
Final verdict: Intended for babies.
http://en.wikipedia.org/wiki/Physical_attractiveness
Specifically search for 'breasts', there's six mentions and they're all relevant.
The whole reason men find breasts attractive is that they're used subconsciously as an indicator of health and fertility. It's not an 'evil society' issue, it's part of our evolutionary history. Breast state indicates age, health, whether the woman has a child and potential ability to feed a child.
Basically there's a damn good reason men like breasts and it's nothing to do with society.
OT: Interesting choice of photo considering it's not just breasts, it's generally a rather suggestive photo.