1."What? a settlement at sea is never going to be totally independent of land -- how will the sea dwellers mine metals, for instance? And if they have constant commerce with land, how will they be immune to plague or war? And as for natural disaster, won't they be dramatically more vulnerable in that regard?", and
2."Who exactly is going to pay for this?"
I expect the second one has had far more stopping power than the first since we started swapping pointy sticks for pretty rocks. I can see it as a sign of our true human origins well after we leave the Oort cloud.
But I agree, just because it can be done, technically, doesn't mean it should (but I still kind of want a solar-powered flying car and a condo on the Moon - I blame Robert A. Heinlein).