Zubrin citisism

Another critism I have for Mars is that because of its difference in
atmosphere and Gravity any colonist immigrating to mars will be
condemning his decendents to permenant life on Mars. Their bones will
not be strong enough to handle Earth's gravity.

Colonists of Space Islands will not have this problem so long as their
colonies stick with a standard level of gravity.

Personally, I do not see Mars as colonizable, so I often find myself
ommitting this argument. Once man reaches into space to nest, there
will be little use for Planets to dwell upon.