No, no and no
You've already argued that corporations can't pay taxes, because corporations are really the people who are shareholders. So you don't get to argue about what belongs to the banks. The banks are people, remember?
Second, a loan is how a bank invests its money. When I invest in a company and they lose money instead of making it, that loss belongs to me. So if a home that is collateral on a mortgage (investment) loses value, that investment has lost value. That belongs to the bank. "But the mortgage holder owes the bank that money!" So? A balance sheet should reflect what investments are actually worth, not what you think they're suppose to be worth.
Finally, "the only impact that has on the paper in question" is how much it will eventually return. You do realize that's the outcome of the default rate, don't you?
