Edit: And of course, what would be the motivating factor for someone to give their best possible work, if the other 12 guys in their position get paid the same for less quality work?
The merit comes from people being able to take risks that otherwise only the wealthy could do
UBI gives that to everyone, giving everyone a shot at developing their merit.
UBI isn’t “no one gets paid on top of UBI for value delivered”. UBI does nothing to limit that motivation.
2. "what would be the motivating factor" They don't, UBI is not communism. And what you say is already true at many places, and the world is still turning. The motivating factor, with UBI, is the same without it: to achieve more. UBI would just let you not fall into homelessness and / or under the poverty threshold.
How do you figure? Why wouldn’t landlords, businesses, etc just adjust their prices based on the UBI amount. They’ll be happy to collect more money courtesy of the taxpayers.
The same reason why they don’t capture all income now: “landlords, businesses, etc.” aren’t one single monopolistic entity, there is price competition in markets for necessities that aren't regulated public utilities. There may at times be (natural or artificial) supply constraints in one or anothet market, but those are (1) separate issues from UBI, and (2) natural poison points which create political pressure for resolution.
I really do like the idea of a country keeping all of its citizens above the poverty line though. If UBI isn't the way, then some other way - maybe providing goods and meals instead of money? Taking a page from the Sikh's book.