To believe this, you must believe that the economy can become arbitrarily decoupled from any physical good. Do you believe that food can become an arbitrarily small proportion of the economy (and so arbitrarily cheap relative to income)? Steel? Purified silicon? Infrastructure like bridges?

I don't. Perpetual growth is incompatible with finite resources. Fortunately, human flourishing does not depend on infinite economic growth; there is, for example, enough food for everyone on the planet. Capitalism is just bad at allocating resources by any metric other than its own. (Yes yes, it's better that feudalism was. I think we can hold ourselves to a higher bar than that.)