Landlords are running a business and get taxed on the rental income of their property. Deducting costs, including interest, same as any other business, is pretty standard and most wouldn't say it's "unfair".
Giving an interest deduction to owner-occupiers is a common policy to promote home ownership. But it's not a "level playing field" with landlords unless you also assess income tax on the imputed amount of rent they are saving by owning.
Giving an interest deduction to owner-occupiers is a common policy to promote home ownership. But it's not a "level playing field" with landlords unless you also assess income tax on the imputed amount of rent they are saving by owning.