The right way to think of a union is as a force with similar (but radically reduced) power over your work conditions, but one with different incentives and for which you have some (depending on how healthy the union is) representation.
Unions can obviously be a bad thing! But the idea that they're intrinsically coercive is a little overwrought. All of employment is coercive; the median union simply peels off some of the coercive forces that apply to your job and hands them to the employees as a collective to manage.