I tend to agree, though this kind of reasoning followed through leads to very nasty conclusions. A fully automated world could eliminate most people, eventually, seeing them as parasites and freeloaders, but who would want to live in that?
People can still contribute in lots of ways which are severely under-appreciated by the capitalist system but appreciated by other people. There will hopefully be a point at which cutthroat "efficiency" and "productivity" is not the only goal anymore. After all, redundant and decentralized systems are more fail-safe, stable, and common in nature.
And the people are there, they may just as well do something... preferably something that makes them feel useful and belonging. Like open source software for programmers, art for creative people, caring for the old and wounded for empathic people, and so on...
Then again I might be a hopeless idealist. In that case, good luck holding on to a piece of the ever-smaller pie. The next round of musical chairs might be my, or your obsolence.