The trouble is that a bank is not lending against the nominal value of the stock as collateral. That number is almost entirely fictional. Taxation of capital gains at time of sale is less a loophole than a reflection of the difficulty of assigning a fair price to assets that are not perfectly liquid.
Also, you'd totally gut retail home equity lending as collateral damage, with disastrous social policy consequences.
Also, you'd totally gut retail home equity lending as collateral damage, with disastrous social policy consequences.