Based upon the logic that providing more welfare with no requirements (aside from PC status) will lift more out of poverty to purchase more goods, then why not provide even more money, and lift all out of the middle class and purchase more goods?
Because in the end, this welfare, which is money and goods without any product or requirement toward being productive and self-sufficient - increases inflation and the Ntl. debt and cost of living for all, thus requiring more income.
“without any product or requirement toward being productive”
You hit an important point. All the constitutional and moral arguments aside, the reason a UBI (or nearly any other form of welfare) does not achieve its purported goals is because it channels limited resources from productive ends to non-productive ends.
A monthly check may improve the daily quality of life of the recipient, but not enough to accrue capital, save and invest, develop new products, etc. It is mostly diluted further into goods and services industries. As another poster said, the recipient becomes a permanent parasite, and is de-incentivized to become more productive themselves.