In fact, to physically print currency, there has to be a backing of treasury notes. "printing money" as a euphemism of "creating money" is not accurate.

But it is in almost every government's interest to debase their money. People have been doing it with gold and with representative money as well as with fiat money.

And Americans have been doing it since colonial days.
http://en.wikipedia.org/wiki/Colonial_scrip

Even countries that want their central banks to control inflation set a target of 1-2% and Congress wanted the fed to consider employment and economic growth as well as inflation.

Also note that the Federal Reserve can create money just by changing the reserve requirements. This isn't money that the government can spend, but it is still very real money in the economy:
http://en.wikipedia.org/wiki/Fractional-reserve_banking