Why not? Aside from violating (unconstitutional) legal tender laws, Beenz would have had no less intrinsic value than the fiat currency used to buy them. They were never a real threat to the Fed.
Now, someone comes up with a gold backed electronic currency, THAT is a real threat to the Fed, and they are shut down rather quickly. Why? Because, unlike Fed notes, a gold backed electronic currency would have real intrinsic value.
There's nothing unconstitutional about legal tender laws, the Constitution explicitly gives Congress the authority to pass laws regulating the issue of legal US currency.
There are gold backed electronic currencies, and a lot of people will tell you gold is more valuable than fiat money, so they will gladly take all of your fiat money and give you some gold electronic currency in exchange. Gold is a crap currency. It's just as "fiat" as dollar bills, except (a) commodity backed currencies are totally ruined by gold rushes, (b) using commodities as currency distorts the market value of that commodity, and (c) a gold standard would lead to deflation, which would be an economic disaster.
All of which misses the main point, which is that you took a discussion of a failed startup from the dot-com era and used it as a springboard into a totally unrelated recitation of half-baked goldbug talking points that are off topic and for that matter rather crankish. Little different than if there was a failed dot-com that centered around teaching kids about biology, and someone commented on it just to push some creationist viewpoint.
(Trying to make up a little for missing the down-arrow and accidentally modding you up.)
Now, someone comes up with a gold backed electronic currency, THAT is a real threat to the Fed, and they are shut down rather quickly. Why? Because, unlike Fed notes, a gold backed electronic currency would have real intrinsic value.