Thanks to Fox News, there is mass hysteria about the Facebook Messenger app being the Worst Thing Ever™, which is silly. The ruckus is all about how the app asks for all sorts of permissions to use the camera on your phone or access your contacts and other assorted permissions.
Now, I'm not one to tell you that Facebook isn't evil. It is, for all sorts of anti-big-corporation, anti-privacy reasons you can Google on your own. It's just not evil in the way that the fear-mongers are espousing all over the internet. (Ironically, it appears that most of the fear mongering is happening on a certain social platform that… I mean come on people. Put your money where your mouth is.)
Here is what you need to know about the Facebook Messenger app:
1) The permissions it asks for are basic to the functionality of the app. Without granting those permissions, why did you even download it? If you want to share photos with your friends via messages, guess what, the app needs permission on an operating system level to even access those photos to begin with. Same with video, same with audio, same with all the other features. On iOS, if you don't grant those permissions (which are enabled on a per-function basis, unlike Android's all-or-nothing approach), your app is a brick.
2) The permissions it asks for are the same permissions that literally every other app on your phone requests. Need to edit a photo with Camera+? Need to grant it permissions. Want to send an email with the Gmail app to someone in your contacts list? Need to grant it permissions.
Speaking of funny cat pics:
4) No, Facebook isn't secretly using your camera to stalk you when you're not using your phone. The fear mongers hint at it, but they won't quite come out and say it. Because it's not true. Stop it.
Now, one thing I should note is that although I have issues with Facebook, I actually really like the Facebook Messenger app. It's fast, allows me to send audio messages (which was amazing when my girlfriend was in Ireland), and works like a charm. Facebook is of course processing everything we type, but they were doing that anyway, regardless of which app I was using.