And this is bad how?
People are somewhat flexible. If they're highly optimized for a particular set of constraints, then the human race is more likely to get wiped out.
This seems like the least of our concerns here. I think a far-flung, spacefaring strain of highly efficient mindless replicators well-protected against all forms of existential risk is still a horrifying future for humanity.
Related to: Kaj Sotala's Posts, Blogs by LWers
By fellow LessWronger Kaj_Sotala on his blog.