A word of caution: I still wouldn't use ACH to debit from bank accounts. You will have fraud/sore casino losers/etc, and your only remedy is to sue. The banks don't get involved with ACH disputes at all because there is no money in it. (Pennies vs a credit card where the bank charges the merchant $20-$45 to mediate complaints.)
Are you saying that all a customer has to do is call their bank and say they didn't authorize it, and the bank takes the money back from the merchant without question?
Does that apply only to merchant-initiated ACH? What about if the customer initiates the ACH from their bank's website? Most banks offer some sort of bill-pay service, which is sometimes processed electronically; some banks offer outgoing ACH directly; many others offer it through a service such as CashEdge's Popmoney.