First, and probably most important, after a male dog has gone through sexual maturity, and is two or three years old, neutering will not change their personality or decrease their drive to aggressively protect properly. Another plus is that neutering decreases roaming and marking by 60 percent.
Neutering also helps decrease dominant aggressiveness over people and other dogs. The no-brainer is the health advantage. Every non-neutered male dog over 10 years old has some form of testicular cancer. One out of four of these cancers is the bad one.
Please listen to your vet about neutering.