I always get a kick out of technical methods like this because all you would really have to do is punch the owner in the face and use his or her fingerprint to unlock the device. It's sort of like the 5 dollar crowbar from xkcd.
If you compromise their accounts from the other side of the world by tricking a fingerprint reader, they won’t know immediately. And you’ll have broken fewer laws, and possibly be located in a country without extradition.