Funding UBI isn't the issue. A sovereign currency issuer can literally create money out of thin air, taxes aren't necessary. The only real limiting factor is a collapse in productive capacity and the attendant inflation. The problem with paying people to do nothing is that it directly reduces productivity because hey why work if you can get just as much money doing nothing? Arguably most jobs today aren't really productive anyhow though. If 80% of HR Business Professionals were instead paid to watch Netflix and look at Facebook, what would change?
This is something a lot of people just don't understand. Our entire monetary system isn't predicated on exchange or store of value like they teach you in school, it's a system of coercion. That sounds ugly, but it's observably true. Taxes, in particular property and income taxes, impose a requirement on everyone to participate in the state's ledger game. The question becomes is that coercion eucivic or not? A society without coercion isn't an option. Nature abhors a vacuum, and human societies abhor a power vacuum. Given our present level of technology, the alternative to monetary coercion is closer to gulags and plantations than it is to Star Trek.
The coercive aspect of monetization is perhaps most clearly seen in the example of imperial British Kenya. When the Brits rolled in they wanted the local to work in the mines. Local Kenyans, quite reasonably, said screw that we'd rather not. The Brits then imposed a head tax on every Kenyan adult payable in Pounds Sterling. And, in that economy, the only way to get Pounds Sterling was working for the British government. So maybe you could get a job as some kind of functionary, but the vast majority of jobs were, you guessed it, working in the mines. In this way the sovereign currency issuer was able to coerce the behavior it wanted, namely the dirty, dangerous and unpleasant work of mining, without any overt violence.