I kindly disagree. Nobody wants to live forever on Mars (if you do, you may as well go live in a bunker and never go out, no need to go there). Nobody wants to live forever in a spaceship (for the same reason).
What does that mean? The goal, what people actually want with the "space quest", is to find another planet. Check how far the closest star is (that's more than 4 light years away): we cannot even theoretically go there in any kind of meaningful way, even in the long term.
If your quest is to become a multi-planetary species, you should do theoretical physics on Earth and try to find a way to go that far. No need to solve the engineering problems first, let alone in a resource-intensive and counter-productive way (w.r.t. our survival on Earth).
I find it amazing that engineers don't find it insane to do all the engineering work for something that is, currently, theoretically impossible. It's like building public transportation all over the world based on the idea that we will discover telekinesis ("it doesn't work right now, but as soon as you have telekinesis, it will be great"). Yes it would be cool, but the only sane way to look at it today is that telekinesis is not a thing.