Do you know how much it costs to launch a pound into space? It's > $1000/lb just to LEO compared to a ground cost of $0.3 to $3.00 for most food and materials. Everything you need to survive that is not where you are going has to be launched from Earth. The expenses to colonize the Moon would be huge compared to Mars because Mars has all the basics and the Moon doesn't. It is the launch cost not the time that matters. It is also the delta V from Earth to reach the destination that matters in supplying material not the escape velocity and that is virtually identical between the Moon and Mars. In the event of a return the escape velocity difference in favor of the Moon is more than compensated for by the ease of local fuel production on Mars.

The Moon is not anywhere near three days away in a practical sense. Look at the actual time it takes to launch a mission to the Moon not the time from launch. If you have a lethal emergency on the Moon the people are just as dead as on Mars in almost any scenario. Think about the portion of emergency scenarios where some failure on a colony could be overcome after months of waiting by rescue from Earth. The only real differences are self rescue by returning to Earth and I think those represent a small portion of the risk space. Launch and return are the biggest risks and they are about the same between Mars and the Moon. On Mars they would have a chance to make use of local resources for all the key raw materials for our civilization. On the Moon they have almost none.

It's an engineering problem not a travel one. You have to have the resources and you need them as cheaply as possible. The Moon can be used as a test bed for technology although on Earth or in LEO is almost as good in many ways. It makes no sense however as a demonstrator colony because every world has different challenges and it is best to start where it is easiest and most interesting. It's an investment in the future and like all investments it should go first to where you expect to get the biggest bang for your buck.

Maybe I'm way off track here because colonization should be a private effort IMO and that's up to whatever individual with the bucks wants. Maybe you are only talking about a base. Everything I said above still applies, but becomes less critical in that case. I look at NASA's efforts as exploration only, but want the highest priority for human missions placed where the scientific questions are the most interesting and the long term potential is the highest.

Regards,
Mark