the whole concept of cryptocurrency is that the individual can do what they like with their own money. They are their own bank, when they make a purchase no-one should question what that purchase was. UBI, the government will control your spending habits, they will be able to track what you spend your money on. These two ideas dont mix at all, like water and oil.
Not sure its the "whole" concept. UBI could be established any number of ways with blockchain technology that would have nothing to do with BTC or any other altcoin. Regardless, the vast majority of transactions are public anyway, and it will not take much effort to pour it all into a dataset to parse out owners, so...
not if you're projecting an ideology onto cryptocurrency and remain inflexible in broadening its potential uses outside of your ideal...
As far as restricting what the token can be spent on to eliminate spending on undesirable goods, people will find a way to exchange the tokens for cash and just buy the stuff anyways. Even if you would only be allowed to exchange tokens with registered merchants, there will always be merchants who would provide an innocent looking good that can then be exchanged for cash, like prepaid phone cards for example.