Good point. Mars would only be better off if the colonies over-engineered their radiation protection. Otherwise anything that gets through Earth's natural protection would probably get through Martian settlements designed to give the same level of protection. It might be relatively cheap to over-engineer (e.g. digging in an extra meter), but it might not.
It might be relatively cheap to over-engineer (e.g. digging in an extra meter), but it might not.
FWIW, while researching my Moore's law essay, I found materials claiming that underground construction was more expensive but paid for itself via better heating/cooling. But that was for shallow cut-and-scrape constructions and I suspect 1 meter wouldn't take care of supernova radiation.
Article on space.com