Once we can make a human-sustaining bubble on Earth, then maybe it would be worth trying to go for Mars. Right now claiming we can go to Mars and either return or live there is just as feasible as us going to and living at Alpha Centauri. It is pure sci-fi. Im closer to getting my legs replaced with robot legs that can outrun Usain Bolt than anybody is to colonizing another planet. Or building a secret base at the bottom of the Marianas Trench.
These 2 tasks can be solved with only the current knowledge, but they depend on the solution of many technological problems that require only a lot of money and of work.
Only a fraction of the huge amounts of money that have been invested now in AI would suffice to solve these problems, if a serious effort would be done towards such goals.
Whether it is useful to spend so many resources on such goals is a different question, but developing the technologies for an almost-closed self-sustaining environment is something that certainly would also generate by-products that would be useful on Earth, not only in interplanetary expeditions.
And you can claim we can make self-sustaining environments all you want, but people have been making such claims for decades and every attempt has failed horribly, so im going to go with it is still impossible until proven otherwise.
There are 8 billion of us. If a few want to make a go of it, you can be sure they will know the ridiculous challenges.
Space travel costs are falling rapidly. The Solar System has vast resources that seem impossible to reach today, but won't be for long in historical terms.
People still die climbing Mount Everest, for no purpose I can see. But I am not going to gripe if people continue making the climb.