A recent post about the Fermi paradox left me wondering about relative difficulties of getting into space, though I don't think it affects those specific arguments.
People establishing a presence in space is difficult but at least plausible-- I'm talking about biological people as we are now, and being able to live and reproduce indefinitely without returning to Earth.
It would be easier if we were less massive, or our planet was less massive, or if we were more radiation resistant. It would be harder if these qualities were reversed, or if we needed a much denser atmosphere.There might come a point where it just isn't feasible for a species to get itself off its planet.
Is there any reasonable speculation about where we are likely to be on the ease-of-getting-into-space spectrum?