If by irresponsible borrowing one contributes to a bust, the rest of us will have to pay for it either directly or indirectly.
The rosy outcomes are easy to see. But there are 60 YO parents that borrow a quarter million from the 401k, then kiddo drops out and moves to Belize instead of Wall Street. That debt doesn’t go away, and they work until death. This is a possible outcome too.
A good balance is hard to find; it doesn’t just affect the borrower.