I think we mostly agree except on our level of optimism about how UBI will realistically be spent. I would argue that my pessimism is extremely well-founded because present material conditions are an extremely strong (if noisy) indicator of an individual's capital allocation efficiency. If someone is in a position to start a successful business, or engage in productive citizen science, they are overwhelmingly less likely to be a net beneficiary of any welfare scheme.

I think there is a pessimistic utilitarian argument for welfare just because people have concave/risk-averse utility functions (of wealth) and it's possible that the dollar-cheap utility gains for people close to zero might outweigh the higher-order costs, but it strikes me as somewhat fantastical to imagine that there might be meaningful financial gains from a welfare scheme, because people with more welfare money might use the money to read a book or start a successful business or something.