Starship Troopers opened my eyes to the idea that other societies were possible, and by presenting it as real and grounded also eventually made me understand how seductive the hypothetical society of that sort could be, but how destructive it could also be to the human spirit. I re-read it every few years and get something different every time. People who write it off as fascist propaganda or whatever are generally just showing their poor critical reading skills, since the society depicted is actually dehumanizing and pretty not great.
Lord of the Flies didn’t do much for me because it was just a not very far off metaphor for my life growing up in suburban Texas. The only difference is the slight exaggeration that they weren’t killing kids outright, but if they could have they would have.