He would like to be able to buy an item online, wait for it to get to him and then say he changed his mind and get his bitcoins back with one click. Or, he'd like to use the chargeback scam, known from paypal, with a small difference that this time the transaction wouldn't have his name on it, only an anonymous bitcoin address.
Consumers love chargeback because they give them an edge over merchants. You won't find merchants complaining about the lack of this option.