Earlier quoted context omitted.
It does seem like a loophole, such funds when used as income should be taxed. Probably more complicated in practice but it does seem like a strategy that runs counter to the intent of taxation laws. And I'd bet if it was a strategy employed effectively by the 99% it would be vigorously labelled as tax evasion and dealt with accordingly
This is not a loophole. Collateralizing a loan against assets does not produce income. It produces cash and an even larger liability. That loan still has to be paid off with separate, regularly taxed, income. Also this is a strategy used all the time by the 99%. It's called a second mortgage. This proposal would mean that taking out a loan against the equity in a home would become a taxable event.
What they are arguing is that individuals should be taxed at the event of first utility (that is, realizing value from the gains). And then the tax is paid, so not paid again, or offset, later.
And what we're really talking about here is individuals using equity loans for the majority of their income.