Net worth, as in property value - mortgages? Most &#x27;middle class&#x27; people have most of their net worth in their principal residence, so you&#x27;d be adding quite a shocking tax bill to a lot of seniors on fixed incomes who own their own house. That&#x27;s the problem with Mark-to-market taxing.<p>You could start added loopholes to your &quot;block loopholes&quot; law, like &quot;If you reside in the property, it&#x27;s tax free&quot;, but then you hit problems like parents given their kids properties as tax shelters, and the like.