I have a history with chained dogs. Snake was rescued from the end of a heavy logging chain in 1992. She had spent the first two years of her life chained to a tree, living outside with no shelter and limited socialization with the people who owned her. I suspect they were afraid of her. Rich worked hard to rehabilitate her and we grew to love her dearly. She always had issues due to those early years. We had to be careful with her around other people she didn't know and around other dogs. I'm no dog psychologist, but I presume that dogs have a developmental period much like that of children and when that development is not positive, it can have long term consequences. Snake had a wonderful life with us and I'll be forever grateful Rich saved her. She would have been destroyed in a traditional animal shelter. Had she remained on that property where she began her life, it's entirely likely that she would attacked or hurt someone at some point. She was a prisoner on the end of a chain on that property for almost two years and we'll never know the psychological toll that took on her.
Beyond the safety ramifications of chaining dogs, there is the obvious and very important issue of quality of life for those dogs. A dog is not a security system. If you want to use a dog to protect your home, bring the dog inside so that he or she will form bonds with your family and will consider your home his or her territory. If you have trouble house training your dog, get help. There are a variety of resources on the Internet to help you with this process and you can also interact with a trainer or behaviorist to get tips. If your dog wants to be outside or needs to be outside for parts of the day, take steps to keep him or her contained in a way which does not involve a chain. You can install a fence, use a pen (for short periods of time) or use a run or trolley line suspended between two points and property installed with stoppers at each end. Dogs who live outside for large portions of the day - or all the time - must be socialized to your family and to other people. If you don't have time to care for your dog, you really should not have a dog at all. If you still love dogs and want to have a dog in your life, consider fostering a dog for an animal shelter or a rescue group to help a dog learn new skills and to prepare that dog to be someone's beloved pet.