@Darwyn
That's a pretty strict interpretation of the constitutional wording there with your mention of coining HAVING to mean creating coins from metal. I'm not sure I think that really makes sense, or even that it would have necessarily been interpreted that strictly at the time of it's writing.
Now if that's your interpretation of the constitution, then I suppose we are at an impass. I simply don't think the term "coin" needs to be interpreted that strictly, and so we will never agree on the rest of it if we disagree on that level. However I'd also point out that if you're going to be that strict in interpreting the constitution, you should also be opposed to paper money too, because that is not coinage, and it's not made of metal.
My interpretation of that is simply that it empowers the congress to create regulations and policies on how the nations money is to work, and exist (and how it is to come into and out of existence). I just don't think there is anything inherently wrong with or illegal about the government deciding to "create money out of nothing" as you keep saying. I just don't think anything in the constitution says that money has to be backed by metal, or anything else in particular.
Outside of constitutional concerns I just don't think it's necessary or even good for the system to have that sort of restriction on it. As someone else pointed out, as the supply of goods and services in the economy and world grows, at some point you will start to run out of gold to back it up with, and your money will begin to increase in value so much that it becomes more or less useless for everyday transactions.
Another danger of having a gold standard that I haven't thought of in some time, but is something that has been tried (fortunately unsuccessfuly), is the danger of private individuals attempting to corner the market on gold/silver/whatever we're using to back our currency. Assuming the government doesn't just seize all the gold in the world/all the gold it can, gold would continue to be traded and sold, right? Maybe even used as currency itself, right? What's to stop some private individuals/some cartel somewhere from attempting to grab enough of it that they can set the value of it? DeBeers does that with diamonds (which are in reality so common on the earth that they should be quite cheap, but because a company/family controls 80% of the supply of them, they can effectively set the value. I also think DeBeers is arguably one of the more evil entities on the earth, but that's another discussion entirely.). Wouldn't that be even more dangerous than something like the Fed which at least has some regulatory oversight? These individuals wouldn't even have to be in or from the United States, hell it could be a cartel made up of other governments!
I'm not saying it's very likely that that would happen, and maybe I'm probably overblowing the danger of someone actually taking control of enough of the worlds gold supply to be able to dictate it's value. But it would, it seems to me, make it easier for individuals and other countries to exercise a potentially dangerous level of influence over our currency, without much we could do about it.
People HAVE tried to corner the market on gold in the past.