On Thursday, House Republicans revealed their much-awaited tax reform legislation. One of its most-discussed features is a modification to the mortgage interest tax deduction (MID): The bill proposes capping the mortgages on new homes for which interest can be deducted at $500,000—half of the $1 million in home loans American can currently claim this tax break on.

Taken in a vacuum, this is not a bad move. But in conjunction with the other parts of this Republican tax plan, it achieves the same t…