A union is a group of people saying pay us more it give us better benefits, otherwise we will go elsewhere. Most of the power is in the employer. A single individual didn't have much power. And it isn't quite the same as choosing to purchase a loaf of bread from a different store. You keep claiming that a union extracts rents above those the market would ordinarily best. But I don't think you've given any evidence that that is the case. This isn't the case where someone thinks that salaries are too low, so they'll open a new business and pay more.