The "classical" UBI argument from a liberal point of view (classical liberal, not US liberal) has typically been that UBI would lower the complexity and by extension cost of welfare by removing the needs to means-test. In Europe, UBI was typically more likely to be pushed by (by our standards) centre-right parties.

For this reason, UBI traditionally was seen negatively by the left, who saw it as a means of removing necessary extra support and reduce redistribution.

Heck, Marx even ridiculed the lack of fairness of equal distribution far before UBI was a relevant concept, in Critique of the Gotha Program, when what became the German SPD argued for equal distribution (not in the form of UBI), seemingly without thinking through the consequences of their wording, and specifically argued that "To avoid all these defects, right, instead of being equal, would have to be unequal".

Parts of the mainstream left today has started embracing it, seemingly having forgotten why they used to oppose it.