Is it true that neutering will take away protective instincts?

Not that I know of. I know it calms the pet down tho. Neutering a male dog for example can make him less aggressive and easier to train. He'll be less territorial and less likely to destroy property to get to a female in heat, but it won't prevent him from being a good guard dog. All our dogs were spayed or neutered and were all very good guard dogs. One of which was a police dog. He never lost his protective instincts.