There’s a very similar question here: Is going to Mars the right choice? I don’t know if they should be merged, meanwhile here is my answer from that question. In short I agree, this is where to go right now. And that where we go next could be Mars orbit, but it could also be the Venus upper atmosphere, asteroids, Jupiter’s Callisto. That if we develop the ability to live in space for years at a time on the Moon then the whole of the solar system will open out to us and we won’t need to be focused on humans to Mars as the only option.

I think the Moon is by far the best place to send humans right now, in other words the approach that ESA and Russia are following. I'll be on David Livingston's The SpaceShow on 27th May to present this approach: The Space Show - news letter

This is my executive summary (I cover each point in detail in Case For Moon - New Positive Future For Humans In Space - Open Ended With Planetary Protection At Its Heart ):

The Moon is our nearest unexplored territory outside Earth. To ignore it is like ignoring Antarctica after the first few landings in the nineteenth century. Why rush humans as quickly as possible to distant Mars, the one place in the inner solar system most vulnerable to Earth microbes?

• The Moon is resource rich, with volatiles at the poles, including water, ammonia and carbon dioxide which could be in hundreds of millions or billion ton quantities, a source for metals including pure iron in the soil, regolith easily made into glass, hard vacuum for chip manufacture, etc.
• The Moon has many advantages for a human base, such as the peaks of eternal light, possibly enormous lunar caves etc.
• The Moon is of great interest for science, with many new discoveries to be made.
• The Moon is far safer than Mars as a first destination for humans.
• There are many places other than Mars to settle and perhaps colonize.
• We don't know which gravity levels humans need for health, or what spin rates we can tolerate. You can’t draw a straight line between zero g and full g effects based on two data points.
• Everything humans need in space is available in the asteroid belt, sufficient to build full g spinning habitats with a thousand times the land area of Earth.
• Terraforming Mars is a far off dream. We are not yet at the right state of maturity as a civilization to see this thousands of years long megatechnology project through to completion. Failed attempts would introduce new lifeforms to Mars which may get in the way of future goals.
• Earth is the best place for a backup and to rebuild civilization. We live in a quiet galactic region, at a quiet time in our solar system's evolution. None of the proposed disasters could make Earth as uninhabitable as Mars, leaving Earth is the best place to rebuild. And if our own technology is the problem, the solution can't be to set up a highly technological society in space.
• As a young technological civilization, we should have protection and sustenance of our planet as our first priority, A trillions of dollars megatechnology “backup” attempt could distract from this. We can use our space technology to protect Earth against asteroids, to move damaging mining operations into space, for solar power, and for scientific discovery.
• Mars has much more potential for surface and near surface habitats for indigenous life than realized before. These habitats could host lifeforms that are vulnerable, for instance early life based on RNA and ribozymes instead of ribosomes, out evolved by DNA on Earth.
• We have protection guidelines on Earth to stop microbial contamination of vulnerable habitats such as lake Vostok (isolated lake below 3.5 kilometers of ice in Antarctica). Humans would not be permitted to descend to this lake at present.
• Mars can be explored from orbit more effectively than from the surface, using telerobotics.
• Humans in clumsy spacesuits don't have special advantages over telerobots
• In orbit, you can “teleport” via telepresence to anywhere on Mars with immersive virtual reality type direct experience of the surface.
• We have miniaturized life detection instruments on a chip, that just a decade ago filled an entire laboratory
  "If such capabilities were to become available, one advantage is that the experiment would not be limited by the small amount of material that a Mars sample return mission would provide. What is more, with the use of rovers, an in situ experiment could be conducted over a wide range of locations." (Page 41 of Safe on Mars)These are now the most effective way to search for Mars life, past and present (as eight exobiologists said in a white paper submitted to the decadal review). With our new much more complex understanding of Mars, a sample return will not prove that Mars is safe for humans, or that humans are safe for Mars. Find out more
• We should return samples from Mars either sterilized or to above GEO, or both, at least for preliminary investigation. It is far easier, and legally simpler also, to return them to Earth after we know what is in them. Otherwise we are left with the daunting task to design for safe handling of any conceivable form of Mars exobiology, based only on our knowledge of DNA based life from Earth.
• If we show that human exploration of the Moon is of value to Earth, this will help human exploration of the rest of the solar system, not hinder it.
• The same open ended principle should be used for all our explorations. Rather than grand overarching plans - we need an open step by step approach. At each stage we learn from what we have found so far, and can adapt and change our goals rapidly.
• Until we know a lot more than we do now, we should not close off future possibilities for ourselves, our descendants and all future civilizations on Earth, but should keep all options open.
• In this approach, planetary protection and biological reversibility are core principles.

The Moon in this vision is a gateway to the solar system, a place to develop new techniques and explore a celestial body that is proving much more interesting than expected. Along the way, we are bound to get human outposts in space, and colonization may happen also.

However, settlement in space doesn't need to be the driving force behind our space exploration, any more than it is the driving force behind the study and exploration of Antarctica. If we try to turn Mars and other places in space into the closest possible imitations of Earth as quickly as possible, this may close off other futures, like the discovery of some vulnerable form of early life on Mars, or better future ways to transform Mars. Whether we attempt this in the future is something best discussed once we have a better understanding of Mars, and our solar system.

For more on this, see my Case For Moon - Positive Future For Humans In Space - Open Ended With Planetary Protection at its Heart (free oline version, currently the most up to date, working on it today).

You can also read it as: Case For Moon - New Positive Future For Humans In Space - Open Ended With Planetary Protection At Its Heart as an article on my Science20 blog, also available online in book format and as a kindle booklet on Amazon.

Case For Moon: New Positive Future For Humans In Space - Open Ended With Planetary Protection at its Heart, Robert Walker - Amazon.com

If you are interested in this approach, you might be interested in the new facebook group: Case for Moon - Open Ended with Planetary Protection at its Core