But we don't see this spectrum clearly. We separate it into a spectrum of non-living things, and a spectrum of living things. I am awestruck and baffled by the existence of such things as Old Faithful, and the Landscape Arch, and the Grand Canyon, and Pangaea. I don't give much thought to how vastly more complicated a virus is than any of those things, and we only barely consider viruses to be living at all. Clearly through history we've thought that humans occupy a very special place in the universe, as some sort of false pinnacle of creation, or the special single creature that deserves human rights, or the very image of God, etc. But it's something else to extend a special mental designation to everything from viruses to the right on the spectrum of complexity.
I think it's because self-replication (as a naturally arising thing out of inert molecules being selected for survival) at some point on the spectrum of complexity, very quickly and steeply takes over for durability as the means of survival. Durability is what determines the sliver of inorganic existence that we observe in the world (we see beaches and mountains, not homogenous mixtures of sand and boulders; we see big chunks of carbon, not uranium; we see planets in exact stable orbits around the sun, not planets that are on a trajectory out of the solar system or into the sun). This very fast tradeoff therefore marks a rather clear transition from non-living to living, and somewhere in that vicinity is where the complexity is too much to imagine as arising naturally, so we put everything living in a special mental compartment that we treat with different standards for plausibility.
Honestly I think that's a pretty useful construct for functioning on a day to day level. It's not only not possible to fit the explanation for life in a human brain, when we begin to approach a realization for how ridiculous it is, we're just left debilitated by wonder and confusion too much to make scientific progress. Just as with cosmology and particle physics, we jadedly refer to things in scientific notation with orders of magnitude corresponding to numbers we can't POSSIBLY fathom in order to make distinctions between things we can equally not understand, it's ok to separate the complexity of life from the complexity of geology from the complexity of everyday objects in our mental approach. But once in awhile it's nice to try to unify it all, to get a sense of the bigger picture, and not lose sight of how truly baffling the world is. It's kind of an ego boost how far we've gotten with understanding it at all.
**Side note: Dawkins in his book tries to make the case that any life anywhere in the universe must arise through the same mechanisms of mutation and natural selection that Darwin explained Earth-bound life with. To this end I think he should have actually been much more forceful in the point that natural selection is not a magical thing that happens on Earth. It is an inevitable attribute of anything in existence, living or not. He does describe 'natural selection' of inorganic clays and streams that may have been the foundation of life on Earth, in contrast to the primordial soup theory, but should point out that anywhere in the universe, the things we see existing more frequently are the things that are better suited for existence. That's all natural selection is. It can't HELP but be a true phenomenon. The only problem is to show that this process is sufficient to explain life as we observe it, which he does very well considering it's a non-mathematical pop-science book.