Well again, in most cases robbers will run with the phone before trying to unlock it. Or they will just find it where the previous owner left it unattended. They won't look for fingers immediately, not would they care about the data in most cases anyway.

Now if this is a theft with agression and they do care about unlocking the phone and they do realize that there is a device lock, all they will see is a numeric pad on the lock screen (I'm talking about Sailfish since the beginning). If they are threatening the owner, I believe they would ask for the code before even knowing a fingerprint would work. And they would still prefer a code over a finger even if they knew. I'd just give them the frickin code.

I feel like we are drifting to very unrealistic situations just to make a point about fingerprint unlock being evil. I mean, those who think a smartphone's fingerprint sensor is high-resolution, scans a full fingerprint, and sends it to any secret services (even with Sailfish) are free not to use it. Again, I wouldn't be overconfident with Android/Google Services, and I have nothing to support that Sailifsh would be more trustworthy, but I do tend to trust them more on privacy. However, the device is still locked with a code, the sensor is just an alternative to unlock without typing the said code and risking having it compromised by sneakers. I didn't think finger-cutters would be seen as an obvious vulnerability in this case. It's also a get away excuse: "Nah, can't give you any code to play with my phone Kevin, you'd need to cut my finger and carry it with you. Play with your mother's phone."

[Edit] Thanks Heik, I'll look into that!