Mars is a single easily avertable project, still actually free for discussion unlike profit-motivated matters like the ongoing deforestation here. Until there's a clear profit to be made from Mars, it's politically possible to make a "ok, let's not" pact.

Why not make it more sufferable here on Earth first, build all sorts of guardrails on existence, e.g. modify biology such that we all have a certain maximum to which the pain knob can be turned. And only then terraform other planets? Why be premature?

This question (your last sentence) has been asked and answered. Basically because the window of opportunity is open now and may only be open for a short time. If we wait, we may lose the chance.

You should read medical studies about people born with or who acquired a lessened sense of pain. It’s quite horrific. I’m not saying all pain is necessary but any pain that indicates damage is. It would be wiser to engineer biology to be more robust and to recover from damage more completely so that chronic pain is not a thing.

Give me some credit, I just said put some maximum on pain, not remove it. Yes it'd be nice to recover from damage better but that doesn't help when you are being predated on, like when there is a torturer to make sure you don't recover or when a parasite like the Ichneumon wasp has its whole lifecycle dependent on eating a paralyzed creature alive from the inside out. If you want a discussion please be charitable, it's no fun if you seem to assume I didn't think at all.