But that's exactly why it is a fair comparison. Because it is acceptable to ridicule and make fun of and demean overweight people. But it's not (though that's subjective depending on who you are talking to of course) alright to make fun of someone because of race or sexual orientation etc.
No one bats an eye at jokes about "those fatties", right?
Not that it's alright to ridicule someone because of their weight, but...
Race and sexual orientation can't be changed, but the majority of people who are overweight are in their predicament because they are just eating too much bad food and not exercising enough, in other words, bad choices. People are ridiculed for the consequences of their bad choices all of the time.
How can you tell that most people are overweight due to environmental factors rather than a significant genetic predisposition?
Because of the enormous (no pun intended) rise in obesity over the last 20-30 years. It's not as if all of the sudden people just started being born at high rates with a significant genetic predisposition to being overweight in America.