[imtringued]

Well, I personally think that the banks profit margins are way too high but let me explain why they deserve to charge a profit in the first place.

We can make promises to each other. Essentially write debt contracts to each other at no fee. The problem is that we trust each other but if we want a more complex economy than a barter system allows, then we need to make it possible for a third party to trust the debt contract. Through the introduction of banks as middlemen they use their resources to check how trustworthy the debt contract you offer to the bank is. In exchange you get money, which is a liquid claim on your debt contract and thousands or even millions of other debt contracts. Thus the bank is primarily in the business of managing risk and the management of risk demands a net interest margin. If the bank didn't make money off of loans then any bad loan would lose the bank money and it would go bankrupt over the long term. In other words, the surplus profit that the bank made off your loan is its reward for correctly managing risk.

>This is why housing is so expensive to begin with.

Or it could be that housing is in high demand and banks offer financing so people have more money but since location is a monopoly, supply never catches up with demand in popular areas. Speculators themselves simply predict that there is sufficient demand for you to be willing to bay $400k for a house. Speculators didn't create that profit margin, it is the monopoly of land that created it and they merely exploit it.