'as custom and tribute demanded' Tribute never seems to me to be a positive thing, demanded is rarely positive too. Semantics perhaps.
People usually only go to war when the they feel unfairly treated. Equal exchange doesn't seem like a really good reason to me, but they did and it wasn't.
The fans of Glorantha, runequest et al have always been excessively fond of trolls and it is evident everywhere, I don't think Gregg was immune to this Uzophilia either. Personally I've never been enamoured with eating my children or someone else's for that matter.