People have a long and intimate history with coins. Some of us collected them as kids, and we all touch and see them every day. Unlike currency bills, we know intuitively that a coin's value is supposed to come from its metal content. That's why quarters are bigger than dimes. As a result, most people have viscerally rejected the platinum coin idea. To assign an arbitrary, sky high, valuation to a small piece of metal strikes most people as a deceitful, desperate act. They are right.
However, the same people have no problem with images of thousands of crisp paper notes flying off the printing presses. The acceptance is not impacted by how many zeroes the bills contain. People simply believe that paper money derives value from the numbers, not the paper. This was not always so. Paper money originally entered the public awareness as promissory notes to pay different amounts of gold. Once people got used to the paper, few really cared when the gold backing was finally removed. As a result, the public would likely have been much more accepting of the Fed printing a trillion dollar bill than the government minting a trillion dollar coin.
Currently the Federal Government counts more than $16 trillion in funded obligations. Over the next 10 years we are expected to add another $10 trillion or more. At no point in the foreseeable future are we expected to approach balance in our annual budget. All of our future bills are expected to be paid by future borrowing on a massive scale. Anyone with an ounce of integrity would have to plan for the possibility that an ever increasing debt rollover is a limited prospect. Such an understanding will mean that eventually someone will get stuck with the bill. How is this any more responsible than dining and ditching?
More important than that is the message America is sending its creditors. By informing them that the United States will not use its taxing power to repay its debts, but will only rely on its ability to borrow more (ironically from the same creditors), it effectively admits to running the world's largest Ponzi scheme. It's a shame that more people can't seem to grasp these very simple truths.