Huh?? How are we all the same now more so then we were in the fifties and sixties? Ever see pictures or movies of that era? Everyone is dressed exactly the same as everyone else. If you walked around with safety pins in your face and green and pink hair you would have gotten your ass beat every single day.
People are always influenced by what is popular so you have an amount of sameness in every generation, but I think the diversity seen in today's culture is 10 fold that seen in days of yesteryear.
When my dad went to high-school, they had nerds and jocks. Now there are preps, skaters, hip-hoppers, emos, goths, punks, etc. etc.
I agree that many chain stores are unsightly and surely have less character then mom and pop businesses, but to say that this has caused some kind of regression in the diversity of people is most likely a fallacy.