Vactationing in Mazatlan is very safe. The locals and political leaders know that tourism is the number one industry in Mazatlan, and they work very hard to protect it.
Whether you are in the Golden Zone, or shopping in the Centro Historico, you will be in sight of a policeman 80% of the time. There are regular police patrols, and they do a good job of keeping everything safe, day and night. You really can walk freely in the streets at night, with no problems.
If you stay away from dark alleys and places that are frequented by criminal elements, you should have no problems with crime in Mazatlan.