Space research and development is a huge part of sustainability. It is literally our only chance to move some polluting industries off Earth, at least long term. (I do not expect to see it happening in my lifetime.)

Reusable rockets are a huge progress in space research. People long thought them outright impossible or impractical. And aside from SpaceX, no one has them yet.

ESA's model of throwing away the entire Ariane at each launch is the very opposite of sustainable. It is an expensive waste of money propped up by French military interests.

(Not that the ULA, the Russians or the Chinese do something different.)