Did you read the article? (You can also listen to it here.) If you want to be logical and consistent, you can’t contract in terms of “promises” or “expectations”…only in property. “Signing away” your right to not be aggressed against would basically boil down to “promising” not to defend yourself or allow any agents to defend you. Should you suddenly decide to change your mind and defend yourself when someone initiates force on you, the only way they could enforce the contract of you simply allowing the aggression to go on would be to force you to sit still. So for one thing, you have this circular logic problem where the act of enforcing the contract (as a remedy to your breaching the contract) is the same as carrying on as if the contract were being honored. So what’s the point of the contract?
But even considering your contract were in some other kind of promise…Rothbard uses the example of marriage. To force someone into wedlock simply because they said they would (but now have changed their mind) would amount to slavery.
And even as far as contracting yourself into slavery, again, it doesn’t work:
The basic reason is that the only valid transfer of title of ownership in the free society is the case where the property is, in fact and in the nature of man, alienable by man. All physical property owned by a person is alienable, i.e., in natural fact it can be given or transferred to the ownership and control of another party. I can give away or sell to another person my shoes, my house, my car, my money, etc. But there are certain vital things which, in natural fact and in the nature of man, are inalienable, i.e., they cannot in fact be alienated, even voluntarily.
Specifically, a person cannot alienate his will, more particularly his control over his own mind and body. Each man has control over his own mind and body. Each man has control over his own will and person, and he is, if you wish, “stuck” with that inherent and inalienable ownership. Since his will and control over his own person are inalienable, then so also are his rights to control that person and will. That is the ground for the famous position of the Declaration of Independence that man’s natural rights are inalienable; that is, they cannot be surrendered, even if the person wishes to do so.