It's not about security
I don't think I know a single person who actually makes an effort to keep their phone secure. The vast majority have a simple swipe to unlock; often a pattern but frequently just the basic "swipe left to unlock" thing. Even those that opt for something more secure rarely have anything more than a 4 digit PIN. And of course, any of these can be easily compromised in similar ways to fingerprint sensors, as well as much simpler ways such as looking at the pattern of grease marks on the screen. Most people aren't looking to lock down their phone from dedicated criminals with plenty of time on their hands, they're just trying to avoid accidentally calling anyone while it's in their pocket and stopping people posting random shit to Facebook when they leave their phone on the table.
Sure, fingerprint sensors are not perfectly secure, but at the very worst they're no less secure than any of the other methods the vast majority of people use to lock their phones. If you're looking to protect valuable company secrets then blindly assuming you're safe because of fingerprints would be a bad idea, but the constant cries that fingerprint sensors are a terrible idea and should all be binned just because they're not the perfect security solution are just silly. They're more than good enough for the use of the vast majority of users. In fact, the biggest problem is that they're actually too secure - if I'm driving and want someone else to mess with the satnav or music I can tell them what swipe pattern to use, but I can't give them my fingerprint.