... Why is this idea building steam?

“It's a confluence of several factors. First, it's such a large tax break," Donald Marron, director of the Urban-Brookings Tax Policy Center, told Reuters in an interview. “And the tax treatment of housing is much more favorable than we provide for most other investments people undertake.” ...

... “The mortgage interest deduction...does nothing to improve housing affordability, its ostensible goal,” wrote Moody’s Analytics chief economist Mark Zandi in The Washington Post earlier this month. “Any tax benefit is simply capitalized into house prices, which rise as the deduction fuels demand. And the benefits go to owners of bigger homes with larger mortgages and higher incomes, who can itemize and thus claim the deduction.” Zandi said that the deduction is worth $1.4 trillion over the next decade. ...