There's one reason I can think of for having an interest-only mortgage, versus renting...the writeoff. If you're paying $1000 in rent every month, that's $1000 out the window and gone. If you're paying $1000 on an interest-only mortgage, you're getting a writeoff. So that $1000 per month might really only end up being $600-700, depending on your tax bracket.
Plus, having a mortgage might be give you just enough of a writeoff to make it more worthwhile to itemize, so you can write off state and local taxes, charitable contributions, real estate taxes. etc.
Then, you do have the peace-of-mind of having your own home. Even if the bank owns most of it, I'm sure that a lot of people would prefer that to renting!