We'll have to agree to disagree on this. Labor, like time, goods, and money, is a resource. Like any resource, it can be exchanged for another, or it can be invested in hope of a greater return. People invest their labor in unpaid internships all the time, in hopes of reaping a greater return down the road. Business owners invest time and labor in a business, hoping for a return. Farmers invest labor in hopes of growing a product. None is a perfect analogy, but your claim that labor is necessarily supposed to be a contractual exchange for wages is unconvincing to me.