Consider the frailty of our planet. The speck of dust that it is compared to the depths of the universe. If we don't start colonizing other planets, and gain the experience on how to do so, we'll essentially become extinct quite rapidly.

Forget the robots. We need the experience in sending actual humans there. This has to happen sooner or later if we want to ensure that our race lives on, after our planet becomes inhabitable.

With all this in mind, it's better to do this sooner rather than later. And why not start in 12-15 years? I hope you can see the value now.