To try new things...
One of the keys to understanding the fallacy of UBI is Zuckerberg's statement that "“We should explore ideas like universal basic income to give everyone a cushion to try new things."
How many people would actually "try new things"? Sure - I few would. But most people in the western world already have the opportunity to do this. Libraries offer free books to read, countless organizations offer free volunteer opportunities, and there are virtually unlimited free courses (even at a college level) available to anyone with an internet connection.
The vast majority of people have the time and opportunity to pursue these options but chose not to engage.
In reality, UBI will enable even more people to simply spend their time to watch commercials (occasionally interrupted by TV programs) and, of course, spend more time in the echo chamber of Facebook. Also,
UBI might work if society were stripped of non-essentials and everyone pulled together to provide the essentials. That's been tried before and while it seems to work on a small scale (e.g. communes, kibbutzes, Amish communities) it doesn't scale up well.
Human nature just doesn't seem to be compatible.