I'm all about boobies but don't need to be reminded of their reproductive purpose any more than I need to be reminded that a cute ass is just padding for a shitter.
Nature has made both breasts and rears into secondary sexual characteristics, designed to arouse the human male. Sort of like the red rump on certain monkeys. The large, round shape of the female breast is not required for milk production, and is lacking in many other mammal females.
At one time, humans favored the rear-entry mode of sexual mounting used by other primates. To enhance this, large buttocks developed. Over time, anatomical changes caused an alteration of preferred style to face-to-face copulation. The breasts started to mimic the large, round buttocks, in order to draw male attention. Guess what: it works.
BTW, there is nothing to prevent males from producing milk with their breasts, and even feeding babies. It's all just a matter of working them puppies with lots of suction.