Is it good to teach my dog to protect me?
Generally speaking no. This can be a cause of stress for dogs and oftentimes the scenarios where it looks like our dogs are 'protecting' us from something or someone is more likely a case of resource guarding, where the resource they're guarding is you.
Even resource guarding, which is common for dogs and animals (including us) to do for one reason or another isn't a pleasant one. And although the idea of our dogs wanting to protect us and vice versa can be nice, it's best that they play the role of family pet, friend and companion rather than protector.
As there are many complicated human-made scenarios where dogs just aren't well equipped to know and differentiate whether they should respond in one way or another, meaning it's better to take the safer side and have ourselves be the ones to protect them and be there for them!