Aviation is currently a small fish because it's currently available to such small part of the population on a regular basis. For those that take part of it it's a major part of their footprint. Scaling it up to more people is very unsustainable. Therefore fossil fuel aviation is unsustainable in a world where more and more people get richer.

> Same thing happens when nuclear is suggested

It's not the "same thing". Nuclear has some sustainability benefits. Bringing back commercial hypersonic air travel seems to have no such benefits.