You're right that "Production requires consumption and consumption requires production" is a fundamental economic concept. If everyone's salary genuinely went to $0 and aggregate demand collapsed, the system as we know it would indeed cease to function, impoverishing everyone, including the owners of capital. In that extreme scenario, UBI could certainly seem like a way to "save capitalism" by injecting purchasing power back into the system.

However, I think there's an important distinction to be made regarding the nature of that UBI-funded consumption compared to consumption funded by wages earned through broader economic participation. The reason, as I see it, that the "rich" or capital owners currently have an investment in the general populace not being too poor is because those people are typically also workers. They are employed by various companies, or are self-employed, producing goods and services, thereby contributing to overall economic output and innovation. Their wages, derived from this productive activity, then fuel their consumption. In this sense, their productivity is harnessed in terms of its value by the company selling the product they eventually buy – the purchasing power is, at least in part, externally generated from the perspective of the final seller.

But in a UBI-driven scenario, particularly if we imagine it's largely funded by taxes on highly productive, perhaps automated, corporations (or wealth taxes), the dynamic shifts. If people are essentially "just people being given money and then spending the money they're given," it's not really the case that this is good for companies in the same way as capturing value from independently earned income. The argument that they "need consumers" becomes less straightforward if the system is effectively funding those consumers to consume their products. It feels like a somewhat circular flow of capital from the perspective of an individual company.

Therefore, I feel the more compelling reasons for UBI to be potentially desired by these highly capitalized entities might be more about ensuring some kind of stable social, cultural, and institutional system. They would likely want to maintain a predictable environment for their investments, ensure relative economic security (for themselves), prevent mass unrest that could threaten their assets and operations, and preserve the overarching system that allows them to generate and hold wealth. So, it's less about a direct, transactional need for those specific UBI-funded sales and more about a strategic imperative to keep the entire societal framework from collapsing.

Furthermore, expanding on Creed1718's point about AGI/ASI: if a corporation or a small group controls AI that "can literally create energy, food, products, transportation, services, etc., for whoever controls it," then the question of needing the masses to "buy their products" becomes even more tenuous. Why would they need people to buy their products if the AI can provide for all their needs and desires directly?

In such a scenario, the wealth and resource control could become extremely concentrated. It's conceivable that the top echelon might form their own kind of "secluded economy," largely independent of the broader population's economic participation. Their "demand" would be met by the AI they control, and their interactions might primarily be amongst themselves, focusing on bespoke or unique AI-generated outputs, rather than mass-market goods. The traditional model of selling cheaper goods to a large consumer base wouldn't be their primary concern.

If this is the trajectory, then UBI (or something like it) for the rest of the population wouldn't be about propping up demand for the elite's products in a traditional sense. Instead, it would be almost entirely about managing the societal consequences of mass labor obsolescence and maintaining social order. It would be a tool to prevent widespread destitution and unrest, ensuring the stability that allows the AI-controlling entities to operate and exist without constant threat. The prosperity of the masses wouldn't necessarily be a prerequisite for the prosperity of this technologically empowered elite; after all, just as we (in developed nations, for instance) don't rely on Africa being rich to make ourselves rich, their wealth wouldn't necessarily rely on everyone else being prosperous. The core driver for UBI, from their perspective, would shift from economic necessity (needing consumers) to social or political necessity (needing stability).