Not at all. It's simple economics. Some large people take up two seats, so they should pay for two seats. Paying by the pound is smart because it gauges according to fuel usage.
If someone wants to bring excess baggage (even if they're wearing it under their skin), that's "excess baggage" that other passengers are not taking on board.
Pregnant women? That's 2 or more passengers!
If an airline decides to waive this under certain circumstances for PR reasons, that's their business.
If you don't like it, get together with like-minded people to create your own airline. Then set your own rules.