Voluntary reasons to have an ASL include people that want to ensure that their monthly bill is capped at a certain level to eliminate the possibility of data, voice or text plans exceeding their monthly limits, or to cap extra spending like the purchase of apps or ringtones from Sprint. If Sprint feels you are a credit risk though or you have had payment problems in the past, they may impose an ASL on you.
The only way around this fee is to enroll in automatic monthly payments. Believe it or not, not everyone has a bank account or credit card account to have an automatic payment hit. There are others, like me, that don't allow any charge to hit their bank accounts automatically. Any billing errors cause too money to be withdrawn, and unless you have extra funds to cover it, it can cause problems with other checks. Those with lower incomes may be in this position.
As the Consumerist points out, this seems like a fee to encourage its customers to enroll in auto-pay. Auto-pay is a benefit to Sprint because they are more likely to get their payment. This, being in Sprint's benefit, should be encouraged with a carrot, not a stick. Give the customer $4.99 off as an enticement or give them some other incentive. Sprint could also simply deny new customers an account at all if their credit was bad without an auto-pay arrangement, but I suspect they'd never consider that.
Sprint has been losing customers faster than its the other big carriers in the US. They didn't fare much better in 2009, even with the exclusivity on the new Palm WebOS devices. Does Sprint really need to be making boneheaded moves like this when they really need to do everything they can to retain customers?