Cannr, I understand what you are saying. And yes, a lot of the time it will depend on the employer. I know someone that just recently had to really really fight with her employer to not do the wage assignment, even though they were illegal in her state. So the employer does have a lot to do with it.
But I would say this - As long as you revoke it, and keep proof that you have revoked it, you will be okay. If you can show that you revoked the wage assignment in a timely manner, and your employer still puts it through, then the employer is at fault. You can contact your state labor board, or a lawyer, and they can get your money back. It's a pain, yes. But as long as you revoke the wage assignment you should be okay. The law would then be on your side.