> I think enshittification, cost externalization, and rent-seeking behavior cancel [general societal benefits] out.

While I agree that the factors you cited are drags on the economy, I think historical evidence suggests strongly that they do not cancel out net benefit to society in general. The fact that poor people today benefit from refrigeration, air conditioning, electronic computers, vaccinations, safe anesthesia, cancer drugs, dialysis, HDTVs, cell phones, and a host of other things that the wealthiest people of yesteryear could not have purchased with all their wealth, suggests that the net trend of the economy has been to produce benefits for all of society, including regular people.

> you seem to agree with incentivizing luxury spending on real goods and services (instead of incentivizing capital gains)?

No, that is the opposite of my original claim. My claim, put simply, is that a low capital gains tax shifts the economy's output away from luxuries and toward meeting the needs of regular people.

> I thought trade doesn't make a zero-sum game?

But resource allocation is a zero-sum game. In any given year, there are only so many productively employable atoms and human hours. If less of those resources are being used to produce luxuries for wealthy people, they can be employed to produce goods and services for regular people.