The norm that you pay if you can means we can go easier on people who really can't. Yes, there is always abuse on the margins. But almost everyone who racks up a mountain of debt makes a good faith effort to repay it. That means that we can make it relatively easy to get out from under that mountain, if you've exhausted all avenues.
Indeed, I think that a lot of the outrage at the credit card companies is not that high interest rates, sudden rate changes, and so forth are intrinsically morally wrong, but rather, that there were no common norms about taking on revolving debt. Norms take a long time to evolve, and revolving debt is a fairly new phenomenon, especially at the mass level, and so consumers have one set of assumptions, while banks have another. (Unsurprisingly, both sets of assumptions are the ones most favorable to the party who holds them.)
Now, as to why I am mad at people who violate these norms and not businesses, the answer is that I am mad at businesses when they violate the implicit understandings that businesses operate under. If Dell disingenuously accuses me of violating the warranty in order to get out of servicing some crappy product they sold me, I am outraged, as I should be--I can and should punish them by refusing to buy their product, and encouraging others to do same. If Morgan Stanley walks away from five office towers because the loans are too expensive, this is outrageous if it was understood on all sides that common practice involves sticking with commercial real estate as long as you can afford to, and perfectly acceptable if everyone knew what they were getting into from the start.
But it doesn't have much reference to what people do. We hold businesses to different standards in all sorts of ways. We regulate businesses in ways that we would consider outrageous if those intrusions were stuck into our personal lives--who among those demanding that we apply exactly the same standards to Morgan Stanley as to people would cheerfully submit to a government bureaucrat telling them not to climb the attic stairs without fall protection, or having their finances audited and the results stuck on the internet for the neighbors to look at?
The bigger the company, the more our expectations for it differ from what we expect from individuals--and the more we feel entitled to meddle in ways that would be outrageous violations of liberty if directed at individuals. These two phenomena are not unrelated.
But even at the level of individuals, we treat business behavior as different from personal behavior. We expect people to pay their credit card debts as long as they have enough assets or income to do so without reducing themselves to penury. But if that same person is the owner of a business that is losing money, no one expects him to pour all of his savings into paying off its debts before closing up shop. Owners may well do so, trying to save the business, or the relationship. But no one thinks badly of an entrepreneur who decides to cut his losses. Which is, in fact, why new businesses find it very hard to get loans, and entrepreneurs usually have to personally guarantee any debt that they take on. It is also why so many investors lied and claimed they were taking out a loan for their primary residence; commercial loans are harder to get.