It's about more than money. Workers should have veto power over management decisions that hurt the business' viability or that would violate ethical values. It is the next inevitable step in human institutional evolution--democracy making it's way into working life.
Some companies don't unions because they are built in. Messer Construction and Gore Industries are two examples. They are employee owned , operated, and managed.
That to me is a separate issue. Anyone with bargaining power can use that bargaining power however they want. Unions are just about giving workers bargaining power as proper stakeholders. If they want to use that leverage to make the company more ethical then they can (just as equity shareholders can use their leverage to do the same). But I'm skeptical that the end result will be more ethical business practices (outside the specific area of working conditions or course). Getting large numbers of people to agree on ethical values is hard, especially when there is a substantive cost.
Some companies don't unions because they are built in. Messer Construction and Gore Industries are two examples. They are employee owned , operated, and managed.