Absolutely there were incentives to ban exit, like North Koreans do today. If it becomes known that exit is a possibility without much risk there would be labor force outflow, because the life under capitalism is just better and more full.

They built the Berlin war to stop that outflow, not for some other reason. You can watch Germans storming that wall trying to escape on youtube. If they were just releasing everyone who is "worthless", then everyone would cosplay a "worthless" person to get released. You prove that you are a dumbass once again.