The 6 months travel time are with current technology, and in a few decades we might be able to have better propulsion systems. It's like saying that keeping the

The 6 months travel time are with current technology, and in a few decades we might be able to have better propulsion systems. It's like saying that keeping the MAD threat alive is expensive because you have to refuel those bombers that circle over the arctic... eventually you find better tech. Also, once the nuke rocket is near mars, it takes only a signal at light speed to re-direct it at whatever settlement you want to target.