I agree that utopian predictions have a long history of failure and should be taken with a Mars-sized grain of salt. However, I would argue that the difference is that there is not likely to be complex life on Mars or any other location in our solar system. This makes it quite a bit different from the North American example, in which immense suffering was inflicted upon the existing inhabitants of the region. If any planet or moon was found to contain life-forms capable of experiencing suffering, I and (hopefully) most people would be against human settlement there.