Question: Why is Fritz the hunchback so openly hostile to the Monster?
Answer:He is an abuser because death and living has no significance to him.
Answer:Likely many reasons. It's a monster that is terrifying and dangerous. Bringing a stitched-together dead body brought back to life is probably an abomination to him, and he loathes and fears it.
Answer: So he could seduce Mina slowly with his hypnotic eyes, Dr. Steward would have been in the way.