This system you are calling ACH is also just called an "eCheck". If you write a check at say WalMart, they just scan it at the register and do an "ACH". Like others here have said: "KYC" know your customer rules make it hard to do fraud this way without getting caught.

People do abuse this all the time, look for the bad check writer program in your county. It's not switching over to ACH, that's how it has worked all along. I recommend Catch Me if you Can by Frank Abagnale.