Is debt sinful? Some Christians would want to tell you that yes, it is. Traditionally, Christian Church was against usury, which was defined as lending money with interest charged. In this context mortgage could probably be considered as sinful. Yet who exactly is sinning? The traditional answer would be the person who charges interest, the lender, NOT the borrower.
Strangely, these types of Christians will seldom talk about the problems with modern financial system and whether it's just or Biblical or whether people should be encouraged to go into debt, but they are all too eager to attack their Christian brothers who fall prey to it.
What about personal responsibility, you'll ask. And don't people who take mortgages participate in this system and encourage it? I agree that adults are largely responsible for their own behaviour, yet one should always take into account the fact that not everyone is equally intelligent and has the same degree of agency as others. It's politically incorrect to say it, but it's a fact. The Scriptures say that the law exists for the lawless, the rules of a just society should protect its more vulnerable members from becoming victims to the machinations of others. Noblesse oblige and all that.
As for participating in the system, the only way not to do it for most of us would be to drop out and become hermits living in a forest. Of course, you can always rent, but there is nothing wrong with the desire to own your own home, is there now?
In general, it's a wise thing to try and avoid debt as much as possible. Money-lenders are not on your side, they are in it for profit only. Buy a second hand car and pay cash. Don't borrow money to go on vacation. When taking a mortgage, don't ask for the maximum amount, but rather vice versa. Live below your means. Yet, stuff happens to the best of us. There can be sickness in the family and job loss. I've heard about people having thousands in credit cards debt which could take them years to pay off. It's easy to judge and point the finger. Yet if you feel this urge, point it at the financial elite first.