Another way to look at it: how do you expect people with zero economic power to be able to afford even a robotic servant?

Social security is beneficial to capitalism right now because people still have economic power. Paying a small portion of the people to stay idle home rather than become criminal makes society as a whole more productive. What happens when the productivity of most humans isn't needed anymore to keep the machines running?

What incentives does the market have to keep people alive when they don't serve it anymore?

None, it's just that "the market"/"the economy" as a self-maximizer process will select robots that feed it. Humans are just no longer the fittest links in the chain.

I'm not afraid of super-Einstein evil masterminds. More of heavy machinery with ant-like features that control the food/energy supply, and one day stop feeding us.

At some point farm land will become more valuable as a source of industrial energy than as a way to produce food.

The problem is not that the robots will refuse to feed the idle meat bags, but that their owners will.