I support crewed (not manned; last time I checked crews could be of various genders) spaceflight, essentially because of the PR value for science. It's wildly impractical; it's true that lots of technologies designed for it have gone on to have unexpected and successful applications...but that would be true of any ambitious science program. Realistically, robotic exploration is far, far more effective and efficient, so these are more or less vanity projects. Like Artemis.
I think space colonies are a completely implausible pipe dream. The incredible expense to make them work, let alone be self-sustaining, dwarfs what it would take to settle the most inhospital place on our planet. In fact, I don't think a self-sustaining colony is possible, barring finding and somehow reaching a largely hospitable world. I do think a temporary colony for the purpose of, say mining an asteroid, could justify the incredible expense, though I think by the time we get to that stage, if ever, robots will be the only realistic choice.
Mars, in particular, is fantastically hostile to human life. Titan would be a much better choice...and it would also be a woefully horrific option. If space colonies are our fallback option, then humanity is doomed.
It gives me no joy to write this. I'm a lifelong sci-fi nerd and I would love to be wrong. But when you look at the science...there's just no way.