Or hey, why not use some of that Sufficiently Advanced Technology to MAKE an atmosphere on the planet?
I think there are some reasons to allow "uninhabitable" colonisation (it's technically possible, there's terraforming tech in the game anyway, everyone likes to have arseloads of planets...) but there are also some reasons not to: sure; with enough technology we could probably do pretty much anything -- terraform gas giants, fire black holes from guns, grow cabbages that glow in the dark -- but one could argue that we
don't do everything we can because sometimes it's not necessary, or it's too expensive, or there are just easier ways of getting the same result. I personally think they've done a good enough job of representing reclamation of hazardous worlds with the extreme colonisation techs. Plus making
every planet in the galaxy habitable would just kill my system...

That said, I guess it
would have been cool to allow it anyway, despite its being a bad idea sometimes -- what the heck, put in that "0-World Colonisation" tech, let it be researched for 50 weeks, and when we have it, let's go and establish small, unhappy, parasitic colonies at exorbitant prices!
That's my opinion, at least.
J.