As for your other point, I guess the issue the lack of a hypothesis regarding basic income. You can't test "basic income" as such, and with such unspecific setup you are sure to conflate rather than illuminate mechanisms of relevance. In any case, it depends on your question whether you need to take income away from anyone. Are you going to start by examining distributive effects? Really? No physisict would test their airflow experiment on a flying rocket, while also trying to measure how he exhaust affects the wind in Costa Rica next week and saying 'something' about the future climate. They would start by putting their airflow gizmo into an isolated chamber - which is, afaik, more or less where UBI experiments are.
Fair point. I guess you could run an experiment where money is simply taken away from people, destroyed and then look at the effect of that in isolation.
Money would majorly come from those who have the greater means to pay larger amounts into the system, and on the hypothesis that bettering the material conditions of those in the lower and middle class will necessarily lead to increasing productivity and thus (and 'thus' is a large leap) greater general income that can partly be paid back into the system in a cycle.
That it is harder to draw conclusions from experiments in biology than in physics doesn’t imply biology isn’t a science. Economics adds the problem that we (rightfully) don’t want to do realistic controlled experiments (would at times be hard, too. Put a few million people in a country with a given law regime, watch for a couple of decades, draw conclusions. Repeat) but again, to me, that doesn’t imply it isn’t a science.
I think it’s more part of the humanities than a science, though.
