To build on what S'task said with a couple other points:
1. Right now the system for currency exchange functionally works in two stages. Change your local currency for dollars, then change the dollars to the currency of the place you're buying from. There are reasonably stable exchange rates, and the way that they change is
mostly predictable.
If you remove the dollar as the stable intermediary, you need more complicated means of exchange. Even the simplest option, transferring through multiple other currencies, means that you are paying a surtax on each exchange that drives up the costs, reducing profits, and making some businesses completely nonviable.
It's not just a matter of finding an alternate means of exchanging value, it's also a matter that
whatever it is you exchange, you're spending more effective value in the process of making the transaction, and that adds up.
2. The dollar has something of an inherent value, because Americans will buy basically
anything, and as the largest economy in the world, American demand basically means there's always a place for your dollar to go back to. Americans aren't just interested in buying anything, they also have the sheer money to actually
do so. That's not true of every nation, and the only one coming close to it (China), is immensely untrustworthy in every regard.
I'm pretty sure the CBO does routinely
factor in the impact of tax cuts and raises; however, you may well disagree with their estimates. For example, they take the position that tax cuts do not generally result in such a high GDP rise as to increase tax revenue in a short term horizon to the level that would have been collected absent the tax cut—in other words, they do not pay for themselves and they increase the debt.
From the above, it follows that cutting taxes is not a good way to decrease the debt. One effective way would be to decrease spending, but I do not see a public will to do this when faced with actual cuts instead of the vague concept of cutting. Another way is to raise taxes (which, the CBO believes, are not so deleterious as to entirely erase the prospective revenue gain), which coincidentally is a plausible way to increase public willingness to cut spending.
Then, bluntly put, they're wrong.
People can theorize in the abstract all that they want, but the major tax cuts of the last 40 years proved that growth in the economy is the path to improved revenue, not tax increases.
