I think you're thinking about this too logically. It's true that people often think logically, but a lot of people, especially young boys, don't. It isn't what the antagonist provided, but how he made them feel. He satisfied their need to feel a certain way. Plus he did provide the first pig (if memory serves) and he had previous rapport (I think he was one of the choir boys).

Civilization was on the edge and he pushed it over.

You should interpret the book as you like.

However, I would point out a few things that I thought about while and after reading. Primates of all sorts regularly kill each other. They aren't necessarily bloodthirsty, but seem to do so to ensure their tribes survival. Resources are probably the main reason why humans go to war. There is a finite amount of them which means everyone cannot have everything. I don't think that aspect (resource scarcity) was well represented, but it's pretty clear that war occurs regularly and that we kill each other in brutal ways.

Lord of the Flies is regularly criticized for its unrealistic depiction and I think it's a good criticism overall, but I don't particularly agree with the idea that humans aren't warlike naturally. It seems clear that we historically are for a variety of reasons and only recently, with society reaching our modern sophistication, that wars are more rare (which isn't meant to imply that this time is better).

Just my thoughts.