Moralists maintain that an income sufficient to cover the necessities of life is a basic human right that should be guaranteed by society as a whole.
The government uses taxation to drive the need for the currency it claims a monopoly patent on in order to provision itself without a revenue stream. This creates a condition of unemployment in terms of that currency until everyone is able to meet their tax obligation. It then becomes necessary to provide sufficient currency to the private sector via spending to enable that.
By spending more currency into existence than it taxes back, the government can establish its monopoly issuing authority over the entire economy as its currency gains use to denominate pricing in commerce and contracts. The US Congress is mandated to do this for “the general welfare” in the Constitution, Article 1: Section 8. Given that one cannot collect what doesn’t yet exist, this mandate established the currency, currently the US dollar, as a self-funding fiat without restraint from revenue.
There is a general economic ignorance in America that has severely limited Congress by imposing demands that any spending it does for the public purpose be “paid for”, which is not possible without removing currency from the economy via taxation, and even then only “after” the currency is spent into existence. This incorrect line of thinking is a leftover from the self-imposed restrictions of the gold standard, which should have been declared unconstitutional but didn’t pose a problem until we shifted from being a net exporter to a net importer in the ’70s.
Any large spending initiative, such as a UBI, is going to run into the “payfor” question as the first knee jerk reaction. It is not relevant to the discussion and shouldn’t be acknowledged as a serious objection. The only limitation to spending into the private sector is inflation, which is where the conversation need to take place. You have my permission to tell the payfor dolts to jam it until they gain a grasp on economic reality with a fiat currency we can never run out of.
