Of course Earth is the best planet. But aren’t you a bit curious about NASA's missions to Mars?

Er. Yes. But not for the reasons you think WE might be.

Been reading about NASA's planned mission to Mars.

This post here is generated from my comment made on article below on the NASA Climate website which asks the question: But aren't you a bit curious about NASA's mission to Mars?

Yes, I'm very curious.

Couple of things - In principle I agree with everything you're casting out as reasons for humans to have curiosity in visiting other planets. But; What I'm REALLY curious about is WHY resources are invested into an essentially hostile planet rather than into working on overcoming similar environmental challenges that are numerous on Earth? Does 'doing it for Mars' mean there's a conceptually different impetus for us there than rather for inventing new technologies for alien environments that may have benefit to us on Earth? What is the pay off for doing it the other planet way instead of looking to say, restlessly search for means of creating comfortable habitats for Humans at the bottom of the Marianas Trench or say in the middle of the Atacama desert? Then I find myself being curious about these issues:

Do the NASA planned missions to Mars include return of the travellers or are they one way missions?

Can you please clarify, because I am befuddled:

NASA is preparing for a manned missions to Mars
SpaceX is preparing for a manned mission to Mars
Virgin Galactic is preparing for a manned mission to Mars

Is this impression I have correct?
Is anyone else planning a manned mission to Mars?

Why are Humans not focusing our incredible resources on ensuring our safe future on THIS planet when there is no other habitable planet anywhere within reach of Earth?