[iav]

Not sure if you are aware, but all forms of interest expense is tax deductible for corporate income tax purposes in the United States, not just mortgage interest. This conforms to codes in other countries. There is no subsidy that is specific enough to rentals or investment properties. And since most of corporate bank lending is secured by all assets (including real estate), mortgage debt is somewhat fungible with other secured corporate debt, so it would be pointless to try to tax one but not the other.

[ineptech]

I believe there is a specific subsidy, but in the "other direction" - that's why you can deduct the mortgage interest on your vacation home despite not being a human and not a business.

I'm aware that interest is generally deductible for businesses, and I'm suggesting that houses should be an exception to that. We subsidize most business borrowing because we want businesses to borrow and invest in stuff, and we should have exceptions for things we want to discourage investment in. Sure, it's difficult to imagine how to keep a giant corporation from finding a way around this, but we have difficulty getting giant corporations to pay taxes generally. It would still make sense to narrow or end the subsidy to discourage individuals and small businesses from investing in RE so heavily, and consider other approaches to discouraging larger corps.

[ineptech]

Fake edit to add: my only source is other comments in this thread, but I believe it's true that the vast majority of rental properties are owned by individuals or relatively small businesses (LLCs and such) via regular old mortgages, where the bank knows what property is being mortgaged and the debt isn't realistically fungible with other debt.