Hatred has nothing to do with it. It's a simple question of economics.
Unions guarantee that labor costs will be higher than they should be. It's just a basic fact. With operations the size of GM, the cost of that over-priced labor is staggering.
Union labor is like barnacles on a ship. Each individual won't cause a noticeable difference, but the cumulative effect is devastating.
Unions are anti-liberty.
Unions are anti-American.