I’ll quote from the official transcripts of the constitution found at www.archives.gov … you can skip over them if you like… I have included the whole thing below the fold…
“To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;”
OK so it says the government can make money, and assign some sort of value to it, and to foreign Coin (Bitcoin == foreign coin here), and set standards of weights and measure. That which is not expressly allowed is forbidden is a basic foundation of our law when it comes to US Government, the opposite is true of the common citizen, anything which is not expressly forbidden, is allowed, providing for our freedoms. So there is NO basis that the US Government can hinder bitcoin, or much of any other legal trade/commerce using ANY alternate form of valuation (barter, Visa cards, stored value credit cards, tokens in arcades, tokens for subways) in the US Constitution, atleast under Art. 1 Sec. 8.
The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings;–And
To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof