Marginal rates are weird because you can compare your marginal rate against every decision, but at that point, you aren't comparing every dollar earned to every dollar spend, so effective rates seem to be more useful (marginal would be useful if I was considering working more, I think). Anyways, as someone with a high effective tax rate, I'm totally fine only keeping 60% (or keeping 40% if we added another 20), if in return we all got UBI.