Now try growing grain indoor with lights instead of just lettuce with no caloric value for multiple years with no outside input. And also balancing crop carbon needs against human breathing needs in a closed capsule without having something like mold or algae or other bacteria from throwing everything off balance because you lack 99.99% of the ecological diversity of anywhere on Earth. Or having access to fossil-fueled derived fertilizers which takes massive amounts of energy to produce without natural gas. It sure as hell doesn't make sense to ship fertilizer from the surface of the Earth to Mars, or water, or really anything other than handfuls of extremely specialized equipment like computer chips or extremely difficult to obtain or rare chemicals or elements. You are going to need sustainability of all your basic resources for years, if not decades, before you ever have a chance of assaying and mining and processing such materials for yourself.

How much enriched nuclear material can we really send up in a rocket at a time in order to fuel the massive energy requirements of such a colony? We sure as hell don't want to send up multiple tons of enriched material at a time in a rocket to potentially fail during launch, and we would need that much energy to build any sort of functioning industry on Mars so it is anything more than a glorified emergency bunker where we send people to die.