German Shepherds are not dangerous as long as they are bred in a safe, loving and caring home that promotes ethical breeding practices. These factors are important in the development of the character of the dog.
Like any other dog, their behavior heavily relies on the environment where they were born and raised during their early years. If a German Shepherd dog is used to a home that neglects them, it may cause some alterations in the behavior such as presence of aggression, passiveness, unsociable behavior, etc. Before getting any dog, make sure that you know about the dog's bloodline and breeding history.
Generally, German Shepherds are known to be obedient, strong, intelligent, loyal, alert and protective. Be sure to get your dogs only from a known and trusted breeder or alternatively, you may opt to adopt a dog. It will really take a lot of time and effort for you to observe how a dog socializes and acts in certain types of situation, especially for dogs who are in the shelters because most likely, they have experienced something traumatic in their life. These will help you know if you need to address any unwanted behavior of the dog through training.