Looking at the piles of malware which litter the Windows PC world and the web, we have a pretty good idea of what would have happened if smartphones were left wide open. Also, Android started far more open than it is now. Over the years been getting more and more restrictive in terms of security because privileges were abused. In the early years Android battery life was particularly bad because of bad performing software.

Even with the restrictions in place, Facebook and other apps have been caught abusing privileges to get more CPU rights and burn up battery life (and get collect user information).