What you're missing is that there's a limit to what contracts can legally do. I can certainly enter into a legal contract that requires someone to eat my feces

What you're missing is that there's a limit to what contracts can legally do. I can certainly enter into a legal contract that requires someone to eat my feces for breakfast, but I bet you if I tried to enforce such a contract I'd be told the law won't do it. This here is why the idea of being able to walk away from a contract doesn't make the contract valid or legal, nor does it prevent the contract from being exploitative. Find another reason why it's not exploitative, because them being able to legally walk away from it isn't enough. Not even the LAW uses such a lax definition.