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<p>You’re getting into an interesting area here. Every single tax law and rule has two broad effects: it generates or eliminates a certain amount of revenue, and it influences the behavior of those paying the tax. The mortgage deduction has the effect of reducing federal income tax income, but it encourages private home ownership. The SSI tax (theoretically at least) raises money to pay Social Security benefits, but is brutally regressive on the the lowest income earners. SSI definitely favors the upper and upper-middle earners. The deduction for charitable deductions reduces income, but encourages charitable giving. </p>
<p>There is no tax change possible that does not have some specific, and frequently unforeseen, effect on the behavior of those paying taxes. One of my favorite examples is the idea of substituting a national sales tax in favor of the current income tax. The rate it would take is a subject of some debate, but there is little doubt that it would have a crippling effect on consumer spending (would you buy that new Roomba if it cost $450 instead of $300?, or television at $1,200 instead of $800?). Regardless, it would have a huge impact on the economy, good or bad.</p>
<p>I’m not a professional economist, and it’s been a while since I worked my way through all this, but here are some impacts that eliminating the mortgage deduction would have:</p>
<ol>
<li><p>Property values would drop, and instantly. It would have the effect of increasing the price of homes on the market, which would reduce demand.</p></li>
<li><p>The construction industry and construction suppliers would collapse even more. New construction would plummet.</p></li>
<li><p>Workers in all the supply chain industries of construction would be laid off – truckers, truck parts, tool makers, nail makers, screw makers, building supply stores, light bulb makers, landscaping companies, plumbers, electricians, carpenters, loggers, sawyers, shingle weavers, paint makers, paint can makers – the list is nearly endless.</p></li>
<li><p>With the drop in home values, people near retirement would find their equity nest eggs plummeting, and would have to either work longer, or have to move in with their families. If no families were available, they would end up as clients of social service agencies.</p></li>
<li><p>All the politicians who voted for the repeal of mortgage deductions would be voted out of office at the next election.</p></li>
</ol>
<p>etc.
etc.
etc.</p>
<p>There are a lot more, but I’m at work (earning money to pay my property taxes, partially subsidized by my mortgage deduction), and have to get back to increasing stockholder value.</p>