Is a car a basic necessity? What about a mobile? Broadband? Netflix/Cable wouldn't be an obvious choice but many will argue it is. Washing machine? What about food delivery for those over 55?
You know those 3-wheel motorized chairs, between scooters and wheelchairs for the elderly ... they are definitely a 'necessity' for some but really quite 'in between' for others.
Once UBI is initiated, the arguments to increase UBI will be unyielding.
The next generations' youth will make arguments about the 'inhumanity' of such and such. They may have a point, but we will be the 'old timers' thinking they are mostly ridiculous and actually voting.
...can we afford that? At this point, probably not. But is it something to strive for?
I think it is eventually possible to get the costs of providing basic needs to everyone (say, through automation) to the point where they can be easily covered by taxes on those who choose to work.
I fear though, that housing is an obstacle to this vision, because in many countries, people rely on housing to be an investment (ex. my parents house is the majority of their retirement), and so the politicians protect it as such, and developers have weird incentives... and so the prices don't go down.
If you cover the basic needs of "everyone", the number of everyone will just go up and up and up until you can't cover the basic needs anymore. Do you think earth can sustain infinite people? There has to be a mechanism preventing people to increase their number to unsustainable levels. The current world already does a really bad job at that, I don't think we have to make this worse.
I think the most desirable world is one with a build-in pruning process, where only the most adapted people survive, thus preventing the number of humans to reach unsustainable levels, while still progressing to greater heights. After all, if you just put a cap on the number of children people are allowed to have you're just going to stagnate. It's better to have a large pool to select the fittest and prune the rest, resulting in the same number at the end, only with much better quality. Historically, war was such a pruning process. But I don't think it was an especially good one.
For one, we are likely to hit post-scarcity singularity on our current technological trajectory before generations of UBI queens can cripple capitalism with washing machine demands.
For two, there is no real "wrong" amount of UBI. Not in an objective sense. 100% GDP UBI would simply imply all wealth transfers are 100% taxed by the government and then universally redistributed evenly by said government. It totally breaks capitalism and removes the profit incentive from everything, but that is basically libertarian communism. Someone would probably argue for it. Likewise, where we are now with 0 redistribution we see the fruits of innovation disproportionately benefiting the rich economically for decades. The consequences of that transfer from the poor to the rich encompass a loss of political and economic influence by the poor and an upward trend in poor health and mental illness.
In the same way people will argue how much free speech, or guns rights, or monopolism, etc is "enough" or "right" is subjective and ideologically polarizing, the "right" amount of UBI will have to be decided by the socities that adopt it. If you have a functioning democracy you should be fine. Though for many nations of the Earth that might be an important first step to consider today.
Historically, human populations that did grow beyond sustainable had to starve to death back to sustainable. If you prevent this by giving everyone free food, that's not really a good thing.
It’s also more fair than dying of starvation because your parents gave you too many siblings.