So you're saying Bob is exploiting Adam by making use of his basement and offering little to nothing in return?
Adam inviting Bob to use his basement, at cost, is a completely fair exchange.
I don't know how much we will disagree in the end. I mostly agree with the concepts that you espouse on some level. That said, I have both been a landlord for several years, and spent some time thinking about these issues and what I could reasonably do to avoid being an exploiter.... and what that even means.
I think the problem here is that many of these things are only easy to define well in very simplistic examples, like we see here. Once you start looking at a real situation, things get murky really fast.
First of all, Adam, in the real world, is oftenly not a free man himself. He is someones wage slave. He is in an exploitive relationship with a bank, who has a lien on his house. Unless he is independently wealthy, or his wage slavery pays him enough to afford the place enitrely, he may, in fact, be risking more than profit.
For example, if Bob moves out, having the space empty may reduce some costs, but, likely its not 100%, in fact, the cost reduction may be more in the realm of 50% or less. As such, any time the space is empty, Adam is in fact losing. Finding new tennants can take time, depending on time of year and economics.... so this is a real risk.
More than that, Bob can cause problems, do damage. As someone who has had to clean up after tennants, and listen to the complaints of neighbors (as often as not, unreasonable complaints).... there are indeed costs, if not always direct financial ones.
What do we include in Adam's costs? Do we include the fact that maintaining his standard of living past his useful working years as a wage slave will require a reserve of money? What about the reserve of money he may need when the heating oil tank leaks (I had that happen last year, over $20k out of pocket unexpected, not something I was at ALL prepared for and left me in a very nasty financial situation), or the roof needs to be fixed, etc.
For a while I kicked around the idea that the house should be owned by everyone in the household... but that makes things very hard if you still want people to be mobile. Not everyone wants to pick a place to live for the next 5-10 years, some people don't want to commit to something longer than a year.... some wont last more than a year before others are saying "its him or me".
I just... don't see how to apply these ideals unless you have a group of interested and dedicated people who want to come together into a commune. Not that I am against this concept but, I have yet to find myself in the situation where I knew enough people who were interested and I would feel comfortable entering into such a situation wtih.... well thats not true.... I met one such person.... and I married her.... but so far thats about it.
Honestly, I think people who look at rents as exploitive discount too much the exploitation of the landlords by the banks. Ive done some basic math crunching and, maybe its different elsewhere but, I look at rents vs mortgages and tend to think things are generally much closer to equity than it may seem.