Facebook is not equivalent to law enforcement (not yet anyway). You don't have to use or have a Facebook account. You also don't have to have the app installed on your phone.
Technically probably not at the moment, but this would affect the notion of intent and increase penalties if you used this information to commit another crime, like murder, burglarly, etc.
Is it illegal for me to stand in the public street outside of your house and note when you arrive and leave and other observable-from-public factors?
Honestly you bring up a good point. We definitely need an update to our laws to specifically address privacy. The Constitution was written when people lived tens or even hundreds of miles from each other.
And wasn't it just recently in the news that all major USA cell phone providers are selling your location tracking data to third parties?