Part of my job as a private dog training instructor is doing a thorough behavior intake on the dog on the first lesson. Often my clients call me for a problem that is small compared to the one they really have, and they are not even aware of it. So it falls on me to tell them, "your dog has an aggression issue, but I can help". No client wants to hear this, especially when they perceived the behavior to be normal. I am often met with hostility, denial, justifications for the behavior, or fear.
Growling is normal for dogs, just not acceptable for a pet dog that the family and their guests needs to trust and be safe around. I understand how they feel, no one wants to hear this information about their otherwise loving dog. This is what I often hear, "he is a sweetheart, a big love, he's not aggressive". When unaware of the behavior being a problem, the excuses run the gamut from,"well, it was a really big guy that Fido growled at", to "all dogs guard their bones, that's normal". I have to tread carefully to bring to light the fact that this is a serious issue that must be addressed without scaring them, or losing them as clients. I offer solutions immediately, but of course, they often want guarantees that this can be fixed, and I can't give them that. Others try to dismiss the problem and don't even want my solutions as in their minds the growling, snapping, snarling was justified. In the dog's mind it is justified, it just isn't safe to accept this behavior in a family dog.
This is why I carefully word the question when I get to the aggression portion of my behavior intake. I ask "has your dog ever growled, shown his teeth, snapped, snarled or bitten someone even if you think it was justified". It took me time to learn to ask this way, and some experience and understanding of people. If I ask "does your dog have any aggression problems", I will never get the info I need. My job is to show the clients the light at the end of the tunnel, and to make them grateful that their dog warned them but didn't bite if that is the case, and how important it is to never suppress the warning the dog gives us. It is important information and communication, and it helps us identify the triggers, thus allowing us to work with them in a positive, solution oriented way.
Most of the time the dogs can be helped, and the behavior can be eliminated as long as the owners are not in denial, and are always aware of the triggers, and continue to use the protocols I set up for solution.
So for the record, no growling, snapping, showing teeth, or biting is acceptable, with the exception of a badly injured dog, or one in the midst of a dog fight. The sooner you can accept your dog has an issue that you need to address, then you can move forward toward solving the aggression issue. Try not to waste time with excuses or denial, though hard to hear and accept, it is not the end of the world, and most times can be fixed or managed, depending on the severity. Your dog still loves you, he just needs your help to be a safe, wonderful pet.