You make good points, but I wonder what "costs" and "resources" mean in the context of a (hypothetical) self-enhancing, autonomous AI. All I can think of is computational substrate and the energy to power it. And once the AI has booted-up its obligatory drone army and orbital platforms, it can harvest very large amounts of both. Without us.

Obviously I'm being alightly facetious, but my point is the constraints on an AI may not be ones we're familiar with as humans (society, environment, etc.)

And again obviously, such a scenario is unlikely. But, like DNA replication, it only has to happen once and then it just keeps on happening. And then its game over for us, I reckon.