It would set a minimum income that everyone would know they had.
Whatever work people did would add to that. It would encourage the unemployed to start businesses, or do casual work as they would keep all the money (rather than having their benefits cut).
How would this differ from the tension we have today between the employed and the unemployed? The latter are already heavily stigmatized (dole bludgers, welfare queens, etc).
Absolutely not. Our current system is closer to that because you lose benefits as your income increases, to the point where in some case it's possible to get a raise and end up worse off. With UBI (assuming it replaces most means-tested benefits), you're always better off earning more.