In theory, the mortgage interest deduction is supposed to encourage home ownership, a questionable goal for government to begin with. The purpose of taxes is to raise money to finance government services, not to manipulate human behavior or economic activity.
-Philip Klein, as excerpted from this article
Unfortunately the tax code has been used to manipulate behavior as long as I can remember. Here of late, the subtle manipulation of the tax code has been used as a fund raising mechanism by the august members of Congress. If you would truly like to get money out of politics, the best first step would be a constitutional amendment stating calling for a "flat tax." Just saying.