Just to keep things in perspective, the goal of Touch ID is not to be unhackable. The goal is to get more consumers to move from zero security to pretty good security. A very large number of people don't put any kind of passcode of any kind on their phone, simply because it's inconvenient. Touch ID is designed for them. It's not designed to secure nuclear footballs. Touch ID is going to massively reduce the number of…
Here's Apple's main marketing text on the subject: > Put your finger on the Home button, and just like that your iPhone unlocks. It’s a convenient and highly secure way to access your phone. Your fingerprint can also approve purchases from iTunes Store, the App Store, and the iBooks Store, so you don’t have to enter your password. It is definitely intended to replace passwords. Pretty good security would be to requir…
My debit card, for example, has "paywave" short range payment support. So anybody who has my card can go around making small purchases, no PIN, no signature needed. I'm fine with this because the convenience far outweighs the security concern.
With the iPhone an attacker who replicates your fingerprint can make purchases to your iTunes account using your phone. They can't purchase to a different account, they can't purchase to a different device. In that sense, requiring a valid fingerprint is more than secure enough — even if faked it's not going to do much damage.
Creating a fake print that can fool the scanner is so much harder than stealing someone's debit/credit card. It's also so much less damaging to the victim (making purchases on their iTunes account vs. making any arbitrary purchase).
I think the balance between security and convenience for this technology is more than reasonable.