For whatever the people who provide the money need.
>There are already plenty of "necessary" people who consume the cultural output of the "unnecessary".
I don't think the corporations/governments will just have a few hundred million people around to add some culture to the place.
>It's worth remembering here that America lost in Vietnam.
Yes but the infrastructure of modern society is extremely fragile. The occupying force (the governments/corporations) already have control of it at the start of the war. The only reason we have so many people is due to this infrastructure. If it was a war where the population was not as fully industrialized, it would be different.
That is not to say the robot owners will win the war, but lots of people would die before then.
>Personally, I'd like UBI, but mostly because I'd use it to free up 40 hours a week (plus my commute, time outside of work invested in a career) for research in fields I'm interested in.
That is what people think they will do, but it is not what they will do. It is not the utopia that they think it will be because there are fundamentals about human nature that mean we don't really just sit around thinking up theories and playing guitar. The people on welfare now do not have that life. They are mostly depressed and subdued, which is the point of welfare.
Humans in general need things like self-determination, the feeling of being valued, the ability to maybe have hobbies that cost more than a basic income. Getting a job won't be easy to make more money, as there will not be many jobs.