Even IF it is true that fat is unhealthy... (and it isn't)
Even IF lifestyle is the sole cause of being fat... (and it isn't)
Those are STILL not acceptable reasons for the things people say about and do to fat people.
Christopher Reeves' horse riding lifestyle choices resulted in him becoming a quadriplegic, yet it would have been socially unacceptable to scream insults at him about horses or paralysis. That's because it's asinine to do so. Well, it's also asinine to be nasty to fat people, regardless of their health or lifestyle.