Acceptance is different than tolerance. If we accept the unhealthy it will become a standard. If we tolerate peoples' life choices they will have higher self-esteem, be better adjusted, and may even seek change independently of berating them. Just remember that people who are hopeless/helpless don't seek change.
I also know heavy-set people who are in better internal health than thin people. I say internal because weight still leads to knee and spine problems. Genetics does play a role, I don't know why there's such a genetic shift though. It's probably a combination of things: fetuses are being exposed to preservatives and injected hormones, increase in fast food due to cultural pressure of "being on the go," increased anxiety (which decreases your body's ability to burn calories), and causal stress-eating.