Psychological factor
IMHO the psychological factor concerning Mars colonization is a bunch of baloney. I know from personal experience that if I'm by myself, far from home in a foreign country then it does not take long before I start feeling blue. However if my wife is with me, the kids are playing nearby and the cat is up on my computer monitor then "I'm home" and it doesn't matter where "home" is actually located. When people go to Mars, they're going to take their families with them (I hope they take along their cats as well).
Gary