Or when choosing a neighborhood that is increasing in popularity (and price) at a rate that outstrips the local average, and you can reasonably surmise that it will continue to do so for at least the length of the investment.
It's pretty simple actually.
It's only situationally bad if you don't know what you're doing.Debt is not inherently negative, but is situationally bad simply because needing debt means you do not have the equivalent in cash. For most people means that you bought something you couldn't afford (property included). It doesn't mean that it is sub-optimal to use debt. I'd mortgage myself as much as I could right this moment if someone was willing to do it. I just don't count as security for a loan, sadly.
General Electric (the largest company in the world) even has to rely on debt (on a daily basis) to cover their operating expenses.
Debt is only bad if you don't know how much you can afford. To a certain extent, and especially when money is as cheap as it is right now, it makes even more sense to say finance a home purchase and lock in those low rates, while using the rest of the money you would have had to use to buy it cash to invest (either in stocks or reinvest in ones own business) and get a better return on that money.