But like Bengal-Stripe above, I am not so sure about the detrimental effects it has on people's health in reality. The amount of Americans I see wearing shoes one full size too big their entire life without issue or the amount of Europeans on the opposite spectrum wearing shoes one full size too small, I am led to believe that much of this is just subjective and down to one's feelings about comfort and fit. There is no right or wrong. There is 'right' in what people who truly know about shoes "think" but then there are too many exceptions to the rule out there who are perfectly comfortable in ill-fitting shoes who go through life without any problems occurring from said bad fit, to create factual statements, IMHO.
Don't get me wrong, I hate bad fit and find it appalling. But I won't go tell someone that they are wrong as it is all subjective in reality. If they ask my opinion, I will happily give it and try to explain why I think that way.
But then there are also those that will never be happy with their fit, even in 10 different bespoke makers' shoes. And those people are just full of crap in my opinion. They are there to simply complain and bother someone else as it gives them some sick sense of satisfaction. Don't waste your time with those people.