Far from being "worthless" Mars is the only really viable place for Mankind to colonise, as it is (in astronomical terms) just next door, and has the potential to be terraformed using current or near future technology, to the point where living on the surface could be possible within a few generations. Contrast with the Moon where any colony would always be confined to artificial structures, and at the mercy of the low gravity (which has deleterious effects on human bodies).
It's all very well the boffins going "ooh look at star such-and-such, it's got goldilocks planets which can support life!" the reality is we are not sufficiently advanced to even consider travelling to any of these.
You say "I think we should concentrate on Mankind on this planet."
Yes, but we are in the classic "all the eggs in one basket" situation at the moment, where firstly, any extinction level event (whether from orbital impact or through our own foolishness) would wipe us all out, and secondly, we are running out of room and resources.
We either need to drastically limit the population growth in some way, or find another planet to move to. Doing this now, before it's too late, would seem sensible. But as you and the previous poster have said "Mankind's short sightedness may well be its downfall".