It is remarkable that pederasty (man/boy relations) are much more distributed compared with homosexuality between partners of equal age. See also Bleys 1995.
In discussions, we often find the following pair of statements:
pro-pedophile> There are tribes with pedosexual relations. See also Ancient Greek.
anti-pedophile> This shows nothing. There are also tribes with cannibalism.
Indeed, I think ethnographical consideration cannot give a general answer how to judge pedosexual relations. But, they can help to find the answer for a lot of interesting questions.
For example, one of the most powerful arguments against the seduction theory is the example of the Sambia tribe.
The boundary between sexual and non-sexual behaviour is very different in different societies too. Especially kissing and touching are often widely accepted, even required. A good example is Afghanistan, where it is common for a man "to display his love for a young son by kissing the boy's penis".