> Bringing those places up to standard doesn't really give you anything new, although it does help those people. Putting humans on Mars is something we've never done before, and could lead to amazing technologies and opportunities for humanity.
I take issue with this. Technological advancement over the last few millenia has been driven by how many smart minds we have at the table thinking of new ideas and new solutions to old problems. To get more folks at the table, we need for them to stop worrying about how to avoid gulags, and get them start training in emerging fields. People in Vietnam studying computer science will bring more technological marvels to your world than sending a rocket and biodome to Mars, the problems of which could mostly be tackled by first building biodomes in harsh environments on Earth, or by finding ways to conquer disease and get fresh water to more of the world's poor.
Build me a sealab and irrigate the Sahara, you don't need Mars to start working on those problems, and those problems could probably help you learn really important skills for Martian exploration (and eventual terraforming) while providing more immediate technological benefits to humanity.