Everything they object to can be dealt with, including radiation and low gravity. If close to 1 G turns out to be necessary for human health, we could build cities as inclined racetrack centrifuges.

Given enough energy, we could not only make fuel in-situ, we could even make plastics out of the Martian atmosphere. In addition, Mars had geologic processes which would produce mineral ores. An entire human civilization could be started on Mars. Historically, this would be analogous to the founding of the United States, just without the smallpox and killing-off the people already there, also starting from more desolate conditions. (Instead of just starting agriculture and industry, we would have to start biospheres.)