Technically I believe the argument for it is even more fucked up ironically social mobility. Without pederasty the relationship to the mentor would be more encouraged along social clan lines and could lead to a rise of effective caste doms. The recognized costs of the shame and protectiveness towards one offspring means the lowest would be more likely to take such "opportunities" as fucked up as it sounds pimping out your sons is the best way to give them a better life.

It has obvious terrible effects involved with it and the very fact it is being considered is a sign that things are deeply wrong but bizzarely winds up a lesser evil in some ways. Which arguably just makes it more insidious which is a whole other moral topic.