I'm motivated to make the world better, not to support any particular policy. If UBI is a good policy, I'm motivated to make it work. If UBI isn't a good policy

I'm motivated to make the world better, not to support any particular policy. If UBI is a good policy, I'm motivated to make it work. If UBI isn't a good policy (e.g. if the expenses or changing incentives would cripple society), I'm not. I think if you reread your post closely, you would see the circular reasoning. You've assumed that UBI is a policy with positive outcomes, as part of your argument for why folks should support UBI. That's "begging the question" (the classical meaning of it).