But let's think instead of who a 50-year mortgage is bad for: someone who can't quite currently afford a house. Who is a 50-year mortgage good for (bearing in mind this is a UK thing): anyone in the business of lending.
It's a done deal that these will become a commonly done way to buy a house.
Edit: at current interest rates this advice makes less sense, but even so, it could pay in some situations. For example maybe your mortgage is 4.5% but your student loans are 7.5%. Take the mortgage and pay down those loans. Obviously too much debt is bad, but not all debt.
Well because the bank never had the money they lent you. Central banks let retail banks invent money for the loans[0]. Then incentives then to meet some thresholds on "affordability tests". If they do that loan doesn't use up as much liquidity as it's face value.
The net effect? You pay your bank interest on money that cost (used bank resources) less that the face value.
[0] https://www.bankofengland.co.uk/-/media/boe/files/quarterly-...
The money supply "increases" when banks lend because of the double entry accounting system. They give you a loan, you can deposit the money in a bank account, and they have more deposits to loan out. It's literally just lending the same dollar twice, not inventing or creating money. (Well... somewhat less than $2 because of reserve requirements).
That's not inventing money.
Since the same money can be spent by the borrower and the saver separately and go off into circulation separately then it is creating new money.
Fractional reserve banking is not how modern banking works. Banks must maintain a liquidity but otherwise the loans are money they made up, they simply tell the central bank they made a loan.
[0] Every sustainable business sells for more than it pays.
[1] Central banks won't make that money available directly to me.
Nobody says you have to make the minimum payment every month and you’re buying with today’s dollars, err…pounds, but paying with future less valuable money. Pay a little extra in the good times but have a lower minimum payment for when money gets a little tight.