Well, let's say you have $300,000 in a mutual fund and are getting an annual return of 15% on it. Then you want to buy a home that also costs $300,000. What are you better off doing?
Cashing out your mutual fund and using it to buy the house outright?
Or keeping your money in the fund, earning $45,000 a year for you, and taking out a mortgage at around 6% interest (which is also tax-deductible)?
In that case I'd argue for incurring the debt. In reality, even though you're incurring an individual debt, you are not "in debt" in the big picture as you'd have a positive cash flow.