So...
If you have a $300,000 loan
And that represents 40% of the property value
in an area that's seeing huge ups in the market
would it not make sense to get a 10 year interest only loan
because
your payment is fully tax deductible (as opposed to renting)
and
in 10 years (at 3% inflation)
your loan principal is 1/3 less than it was when you started.
Why exactly is this a bad thing?
Because "trees don't grow to the sky" and these house prices are now getting to the point where buyers can barely afford the monthly payment during the "interest-only" grave period. So, your choice is either to refinance at a fixed term you can't afford or cough up the remaining principal in cash or lose your down payment.
Even if you have the cash in the bank, the "interest only" loans hurt you because you had to bid against burger flippers at McDonald's who could afford (temporarily) to borrow $500,000 with the interest-only loan gimmicks. That easy money has the effect of inflating the true market value of the house
If you have purchased a property at a non-inflated price and can pay the pricipal off in cash whenever you want, then interst-only loans are just a cash flow management tool.