Yes and no.
It is acceptable in this country to discriminate against middle-class WASP males and overweight people. I happen to be both.
I haven't flown in a number of years as my job no longer requires it. But even 10 years ago, when I was considerably lighter, it was difficult to fly.
I really don't have a problem with this policy, although it might prevent me from flying. I DO have a problem with being told after I'm on the flight that I'm going to have to pay for another ticket.
And to the smart-@$$e$ that say it's just a matter of not eating so much, you're just showing your ignorance. For many that's the case. But for many there are health issues involved, including compulsive disorders, depression, etc. Ultimately it is a lifestyle choice and lifestyle learning. But to say it's "easy" is just stupid.