In a few decades our science and technology will be so advanced that it will be easy, cheap and safe to send humans to space. AI will bring abundance on Earth and a lot of people may become bored, so, why not do some crazy thing like go to another planet? But to follow Elon Musk's inane dream is too early. Someone may say the clock for a catastrophe is ticking, but we can wait 50 or 100 years. It is possible, though, that a man made extinction can happen in this time (like a engineered virus), but it will still be much easier to build self sustained "colonies" on Earth than on Mars. The proponents of this plan should stop telling they are doing it for humankind, and admit it is just for fun. And, as I said, there is the problem of the second generation on Mars. We have no right to force people to live in a place that looks like hell. I do not see people discussing that.