> This is counteracted by the fact that employees now have the option of walking away from their jobs

I don't see how either a UBI or a job guarantee limits employees from walking away from their jobs. The presence of a job, or an income, hasn't stopped many people from starting their own thing.

> But either way, I think a UBI is necessary so that people have the option of working for themselves rather than being forced to answer to someone else.

The option to work for yourself isn't taken away by a jobs guarantee. I can see how the presence of a UBI would permit people to do things no one would pay for otherwise. As idyllic as I really do think that sounds, I suspect that examples of people doing things no one would pay for would be used over time by UBI opponents to drive down the value of the UBI to below a living wage.