the $$$ used for researching and constructing a space-travelling vehicle that can transport humans to colonize other planet, and the amount of effort to transport people and materials blablablablalbla combined - we might as well use the $$$ to re-condition the earth.

plenty of land area for humans.

funny thing about humans is that instead of conquering the wild areas of the land we're thinking of colonizing Mars. and others.

if only humans learn to conserve and plan out for nature and also learn to live on areas in the ocean and wild, then i think it's not an issue.

sorry, i'm digressing from the SPACE TRAVEL topic.

anyway if space is concerned, then i think forget about colonizing planets. if we're having a space ship, might as well have it to be able to sustain humanity.

example - those see in Macross or Wall-E life onboard a space unit.