Well, it's not as though we don't have organisms that live under extreme conditions on my world, but they're generally only on the microscopic level, are the only ones living in that ecological niche, and cannot really survive well outside that niche. Furthermore... yes, we have genetically engineered organisms through centuries of breeding, but it's less to ensure that the species survives in the first place and more so that we can develop breeds for specific purposes.

I think the problem with my view of things, more or less, is that these environments are fairly limited on my planet, and therefore we don't have a reference for life existing in more extreme environments that cover an entire planet rather than a small, specialized niche. The rest of the solar system seems to have planets with conditions closer to the ones you're talking about, but as far as we know, it's really just Earth that can support life. Of course, I don't care much for technological matters so I can't tell if there have been any strides made in that area, but I'm sure you'd have to be living under a rock not to hear if life on another planet or moon within the solar system had been found.