Thanks y'all. Every single issue my current dog (a 6 year old shelter doggie) ever had to deal with was from lack of proper socialization. He was penned up in an outdoor run for the first year of his life and taught NOTHING. So socialization is huge to me. He is a 1000x better than when I adopted him, but I often wonder what his personality would have been like with proper socialization.
And Oko, you bring up a great point about healthy puppies being raised by responsible breeders. The only puppies I've personally known to contract parvo fell into several undesirable categories, which are not mutually exclusive.
-Taken from mother and litter too young
-From a BYB
-In poor health or not properly cared for by the breeder
Obviously I'm painting parvo-affected puppies with a very broad brush, but again, I'm speaking strictly from my personal experience.