Lifeboat Theory--my 2 cents
If I understand the theory--create a human population on Mars in case of extinction on Earth, then it is not a good reason, BY ITSELF, for colonizing Mars.
Obviously, if we had the technology for transferring the huge number of people to Mars required to create a viable permanent population, not to mention the technology required to support a permanent ecosystem, then we would be able to easily use the same technology to divert any approaching asteroids large enough to create an extinction scenario.
There are a lot of reasons to go to Mars, but I don't think this is one of them.
