I believe that there is a school of thought that breasts evolved to reflect the buttocks, and the lips, the labia, once we were walking upright.
Even if this is true, is it right to introduce pubescent boys to the idea that breasts are there for them to find attractive? If it is hardwired then the boys will find that out on their own, and if it's not then you are introducing this idea that women exist to be visually attractive.
Surely given the level of male violence it is important to instill in boys that women do not just exist to give them pleasure?