How many hundred dollar bills do MOST people possess. Two or three, maybe ten. Wonder why there are almost as many hundred dollar bills in print as one dollar bills. Answer seem to be relatively simple. They are used by people skirting the law. Not paying taxes, drug dealers or any type of crime from domestic to international. Suppose the first of the month the US announced that the hundred dollar bill will no longer be US tender in three weeks. If you have these bills you can spend them, deposit them in your account or exchange them for smaller denominations. Those folks using them for any illegal purpose would have an issue. Depositing or spending anything over ten thousand dollar in cash would have to be reported. All the hundred dollar bills being used illegally would be worthless in three weeks. How would they fund their illegal enterprise without cash. It would be interesting for the government to see the rats run all over the world.
This wouldnt solve anything, no one breaking the law would be affected by this. and would just make life more complicated for people who dont trust or use banks. Cash really isnt the right thing to focus on here. It doesnt matter what the currency is, crime is still going to happen.