If I can soapbox for a moment, I think you might be framing space colonization wrong. The big upside to me is that it will give us powerful new capabilities in space.
If we reach the point where Mars has a worthwhile industrial base, Mars becomes the launch pad for just about everything. The weaker gravity combined with the thinner atmosphere (so you can fly vacuum optimized engines from the surface) makes it a good order of magnitude cheaper to launch mass from. For large structures destined for Earth orbit, it would eventually make sense to build them on Mars and fly them into Earth orbit.
By analogy, colonizing the Americas was a pretty bad deal at first. The colonies took a ton of support and it was really hard to bring any value back. In hindsight though, it was one of the most profitable ventures ever. New technologies created exponential gains from the raw ingredients found in the new world.
Orbital manufacturing is also pretty important. Made in Space is working on producing ZBLAN fiber optic cable in orbit, because gravity causes artifacts which degrade signal quality[0]. This seems like a narrow niche but I think it's not. Think about microchip fabs and turbine blades. There are a lot of high value high tech processes that could likely be improved by either the removal of gravity, or the choice of arbitrary levels of artificial gravity <1g on rotating structures. Interplanetary radiation is an issue now, but it's one that can be solved with a bigger mass budget.
I suppose my main point is that this isn't space migration, it's colonization, with all the profit-motive and empire building that word usually comes with.