They do it because currency is used for trade. However, that currency is backed by the securities (i.e. debt). "Money" and "Currency" are two different things in debt-based economics (even though they're treated the same almost everywhere. "Money" and "Currency" are only equal to each other in an economy were the currency is not issued against debt (none exist like that anymore).
Debt-based money is actually the verbal and physical promissory notes that are entered into within an economy. Some currency is issued against these notes and used to pay for things - however, that currency is not money - it is backed by money (debt). [Yes...I know...that definition would get me laughed out of the Ivy League schools...but it is how things work in reality]. You keep wanting to believe that central banks issue money. They don't. They issue currency.
When the bureaucrats in Brussels finally get the OK to issue Eurobonds, the last shreds of monetary discipline will be lost. That is, of course, what they want. The permission to print freely.
Actually, things would improve dramatically - for a time - in Western Europe if they issued Eurobonds. That would give the Eurozone the ability to create massive amounts of new debt in order to pretend they're not in a deflationary spiral.
M1 has increased by 60% in the last three years. That's real money in circulation that the Fed has created or enabled to be created despite your insistence that it hasn't. Are you going to sit there and tell me that the stock markets aren't in a bubble?
Take a look at the Fed's H.4.1 report for July 18, 2013. Go to section 8 and look at the Liabilities section of the balance sheet. You'll see that there is roughly $1.15 trillion outstanding in Federal Reserve notes (currency). You'll also see under the Assets in Section 8 that there is roughly $2 billion outstanding in coinage (as a side note - do you find it curious that coins are assets, while FRN's are liabilities?).
The latest M1 chart is shown to be roughly $2.6 trillion. In other words, there are a lot of bank deposits that are the same currency (physical and/or electronic) getting reused to fund new debt. I.e. - I sign a promissory note. You give me $100. I deposit that in my bank. My bank reuses some of that to fund a new loan, etc., etc. etc. The checking deposits are showing up due to new debt creation - not from the Fed pumping the currency supply.
Yes, the equities market is in a bubble. Companies are doing stock buybacks, which is lifting the price of their remaining shares outstanding. The market will correct when the Fed removes the heroin of QE.
Wish I'd had some real estate to sell you in 2007.
I wouldn't have bought it. I saw this coming (in fact, wrote about it). I went entirely to cash in December 2007.
You can stop right there.
The American dollar is backed by nothing. Once upon a time, it was backed by gold. You could march up to the teller's window and redeem your paper dollars for their defined weight in gold.
Until I can do the same with these securities; to claim that my dollars [either of the "money" kind or the "currency" kind] are "backed" by them is untrue.