I think this reply says it better: https://news.ycombinator.com/item?id=32934162
In short, I think from a humility standpoint that's probably not the best solution. I think there's value in preserving animal life, and also they really help balance Earth's environment which we don't understand well enough nor have adequate industries to replace yet, I believe. If we're going to live in Caves of Steel anyway, why not reserve say 50% of land for wild reserves? Do you want to have paradise and however many billion people you can fit in a planetary steel maze, or do you want just one single planetary steel maze with twice as many individuals? I think the answer is the former, pretty clearly.
Also, in the long term we do have other planets we can build planetary scale steel mazes unimpeded, like Mercury -- I'm sure we'll be able to within a few centuries if we don't destroy our ourselves and our environmental sustainability (which I'm rooting for, and believe we have good chances).
https://www.youtube.com/watch?v=g3g9_dnjaFY