The unique characteristic of a colony on Mars, Venus or another planet would be that it is not on planet Earth. Antarctica on the other hand has to compete with all the places on Earth that are a lot nicer.
There are abundant resources in free space, from hydrogen gas to metals, carbon, oxygen that can be mined from passing asteroids (you could easily live in those asteroids while mining them) ... Energy is plentiful, the more complained about problem really is that energy is far too plentiful.
Maybe you'd want a base on the moon, but free-floating in space would work even better.
[0] https://en.wikipedia.org/wiki/High_Altitude_Venus_Operationa...
Critically, it gains us raw materials. Space is empty. The upper atmosphere of Venus is full of elements we can use to sustain life.
That doesn't seem like a great resource. If you value CO2 so highly there is plenty right here on earth that nobody wants and people will actually pay you to remove from the atmosphere. No need to go all the way to Venus.
Even on the surface of Venus, inhospitality notwithstanding, the resources are at the bottom of a gravity well equal to earth's. It is way more viable to mine asteroids than mine a planet, especially a planet like Venus.
Mining other planets is only interesting if the market for the resource is on that same planet, or we've exhausted the supply of asteroids with that resource.
I'm not sure what that gains us over just having a habitat in orbit though.
Colonizing other planets doesn't make much sense to begin with yet. We don't even colonize Antarctica, and it's a paradise compared to mars.
I'm more interested in setting up industry and habitats in earth orbit. Close enough for low latency internet, and trips measured in hours, but far enough to allow asteroid mining, 24/7 solar, manufacturing and refueling largely outside of earth's gravity well. Plus if something goes wrong you can have escape pods that return to earth. Having a strong space industry like that is also the best protection from potential asteroid impacts.