There is a whole category of financial behaviours, which include non-ethical investments and ultra-efficient tax arrangements, that I have always been ambivalent about. It should ideally be that nobody undertakes such things. But is it reasonable to think that people will spontaneously choose to act against their best interests in a society that is almost entirely unaffected by their personal, specific acts?
It's really very similar in that regard to acting in any other "tragedy of the commons" ways, such as anti-environmentalism or buying from non-compassionate farming. Ideally, we'd all always choose the most alturistic path. And there is good evidence that when the effect of that alturism is personalised and direct, we do. But when the beneficiaries are indirect and our personal impact is minute, we often don't.
The answer, surely, is that this is exactly what the legislature is for. If a behaviour harms society, legislate against it. In this specific case: either don't allow multiple home ownership or impose incredibly strict rent controls and tenants' rights. Then you aren't relying on the good-will of the rest of the world.
In the meantime, I find it hard to condemn as a class those who have to survive within the system we have from making the choices that allow them the easiest ride, even if I can easily condemn specific manifestations of that behaviour.