In pokemon Blue, people think the Rival is Evil. But when you go to the city with the pokemon tower (where they put dead pokemon, think its Lavender town). Your Rival doesn't have his Raticate anymore. He visited the town to bury his pokemon, guess who killed it. You, when you last battled him. His Raticate was in fatal condition. He never blames you, though. And uses this moment as motivation for his dream, to become the pokemon master. At the end of the game, he achieves his dream, but only for a brief moment. where you come and take it all away. Then when you are the pokemon master, his own grandfather (Oak) praises you for winning and scorns his grandson.
You killed his pokemon, took his dream right from under his nose, and even took the love of his only family. You were the bad guy all along.