How and why did pederasty shape Greek culture?

Pederasty was a particular form of erotic association among aristocrats, occurring between an older man, called an erômenos (lover) and a youth just on the cusp of puberty called an erastês (beloved). Although the relationship was defined as erotic, in the sense of having some aspects of sexual attraction, and often being based on the physical attractiveness of the youth, the only social acceptable sexual act was intercrural or interfemoral (the erômenos inserting his phallus between the thighs of the erastês); actual anal penetration was reserved for interactions with prostitutes, something not considered a form of pederasty. 
This practice was as much a result of extreme gender role distinctions and segregation as a cause. Because men would have limited access to female companionship, their erotic impulses tended to focus on other men. This was exacerbated by Greek marriage customs, in which men tended to marry in their thirties, when they were economically established, to girls just entering puberty (normally age 12 to 14); often men would only associate with their wives for the sake of engendering children. 
Formal education was limited in Greece. Before the advent of the Sophists, education was limited to rudimentary knowledge of reading, writing, arithmetic, gymnastics, and music. More advanced education was handled by a form of association (sunousia) of a youth with an older, wiser male mentor; often this took the form of pederasty. 
Pederasty was also an important element of Greek military tradition, where it was believed that male lovers would fight more bravely because of their feelings for their lovers.