We should colonize other planets for their resources

There's an old joke, described more fully at http://www.snopes.com/humor/jokes/moonshot.asp , that appears to have started with Johnny Carson in 1969. The short version is that a Native American recorded a message to be taken into space - "Watch out for these guys [US astronauts]; they've come to steal your land."

This link did not address a couple of important issues:

1) What resources are worth the expense? While there are ideas about platinum from asteroids or 3He from the Moon's crust, resource extraction from another planet is tremendously more expensive.

2) "..., it's probably best we ditch this planet anyways, along with everything on it." ... And what of the 7+ billion people? Leave them to die?