Should you go to Mars? ft Bill Nye

With the ongoing advancements in robotics, the greatly expanded costs and risks of sending humans, I don't see how it would be worth in any reasonable scenario in the foreseeable future. 

What happened to colonies in space?

Large spinning cylinders, say 2 miles in diameter and 4 or 5 miles long could provide a livable habitat inside the size of a small town with centrifugal force replacing gravity.  A second encapsulating cylinder could provide protection from cosmic radiation and most meteors.  Having debris cabled to the outside cylinder could provide additional impact resistance. 

Overcoming Earth's gravity is the major expense getting into space.   Once you have Earth orbiting colony construction supported by mining on the moon, you can the really start to look outward to exploring the solar system.  Technology should be evolving rapidly at that time.  No longer would humanity's existence be threatened by a large meteor impact.  Solar orbiting colonies would guarantee any foreseeable accidental/natural mass extinction of life as we know it for millions of years.  Of course, some other higher lifeform might consider us an expanding plague on the Universe, in which case all bets are off.

Once in space, traveling between colonies would be relatively cheap, as would further space exploration.   Travel back and forth to Earth would be very expensive in comparison because of the gravity tax. Colony size would become larger and more Earthlike.  If the Earthlings continue their destruction of their environment and propensity towards killing other Earthlings with unacceptable thoughts, behaviors, or appearances, who would want to visit?