At minimum, you can argue it's game theoretical insurance.
If Starbucks is so magnanimous towards their employees today, they may not be that way tomorrow.
Corporate advocates for itself. Unions advocate for the employees.
Ideally, they strike a balance so that nobody's satisfied and the best compromise is reached.
Discarding unions leaves the door open for an imbalance of corporate power. (And, since corporations tend toward monopoly these days, that's a lot of corporate power.)
If Starbucks is so magnanimous towards their employees today, they may not be that way tomorrow.
Corporate advocates for itself. Unions advocate for the employees.
Ideally, they strike a balance so that nobody's satisfied and the best compromise is reached.
Discarding unions leaves the door open for an imbalance of corporate power. (And, since corporations tend toward monopoly these days, that's a lot of corporate power.)