Interesting Article. I think a lot of people misunderstand the word Socialize - looking at it from a human context (we go to a party, we socialize, how so.... by talking and shaking hands and hugging other people.), but dogs are not people. I find exposure to be a better word - let them be in the environment, see the people, but he does not necessarily have to go up to each person and greet them. Calm, Confident, Aloof.
In theory, we are supposed to be the dog's Pack Leader, then together we are a pack. Dogs and wolves are genetically 99% identical, and wolves will kill approaching animals that are not a part of their pack. So why do we force our animals to meet strangers with physical interaction (petting)? Sure we all want a Balanced dog who can be around other people, kids, environments, but we need to consider how we we expose our dogs to that. Even then not all dogs are meant for those conditions, and some dogs simply should not be forced into them.
It IS okay to say No. You can simply say "My dog is in training, sorry you can not pet him". Furthermore, the more a pet owner can educate themselves about dog behaviour, the better they can understand their dog and judge how to treat different scenarios.