I guess I'm a contrarian when I say:   Even after a massive global thermonuclear war, Earth will still be FAR more habitable than Mars even with tax men and cluster munitions or tank crews.  If you have to dig underground on Mars, you could dig underground on Earth and probably avoid all the tax men, cluster munitions and tank crews just as well.  If half as much money was poured into surviving post-holocaust perhaps underground on Earth, I think that would be money better spent.