It would lead to increased demand for goods poor people consume, and decreased demand for goods rich people consume. It’s a continual wealth transfer down the hierarchy.

In the short run the increased demand would probably lead to increased prices. In the longer run it would lead to more market investment, more production, more innovation, and by those two factors, lower prices.

Now if your basic income takes the form of newly printed money, that’s a whole new thing and would suck a lot.