Obesity is an ethical issue, because an increase in weight by some imposes costs on others... [a] way to achieve the same objective would be to set a standard weight for passengers and luggage, and then ask people to get on the scales with their luggage. That would have the advantage of avoiding embarrassment for those who do not wish to reveal their weight...the point of a surcharge for extra weight is not to punish a sin, whether it is levied on baggage or on bodies. It is a way of recouping from you the true cost of flying you to your destination, rather than imposing it on your fellow passengers.--Peter Singer [HT Feminist Philosophers.]
I'll leave it to others to dissect the use of racialized/gender stereotypes [e.g., "a slight Asian woman" vs "a man who must weigh at least 40 kilos more than she does"] by Singer in the piece. Let's also grant Singer that air travel is not a "human right" (and stipulate that Singer could grant some exceptions). In effect, Singer advocates differential pricing. This is not uncommon: in higher education Stateside we are familiar with tuition discounts ("financial aid") based on, say, need.
Singer ignores need or ability to pay entirely in his analysis. It is unclear why that ought not be included in this "ethical issue." Evidently, "true cost" does not mean subjective utility. Need is not irrelevant to Singer's proposal because Singer talks about "true cost of flying" without calling attention to all the subsidies offered to airlines, airports, and aircraft manufacturers by the general public (Singer uses the vocabulary of "public transport" without irony by the way); these may well involve non-trivial financial transfers from the poor to the middle classes and rich. Given that Singer selectively focuses on body weight (and shapes) when talking about "true cost" of flying, one cannot help but feel that he is selectively using (Euro/US-centric) upper-class moral sentiments to advocate policies that will disproportionally impact others.