Why does Facebook Messenger need access to your microphone?
If you want to voice call a friend through Facebook Messenger, the app will need permission to access your microphone, because otherwise it wouldn't be able to hear what you're saying and neither would your friend. The microphone is also required for recording and sending video clips with audio.
Can Facebook Messenger call my contacts without my knowledge?
You'll need to give Facebook Messenger permission to directly call phone numbers if you want to use the app, but it won't do so without your knowledge. What the permission actually does is allow you to call a Messenger contact by tapping on their phone number.
Can Facebook Messenger text my contacts without my knowledge?
Facebook also requires permission to edit, receive, read and send SMS messages, which is understandably confusing, but you can rest assured that the company isn't going to send your friends messages without your permission. The app needs you to allow it to have control over messages to allow you to confirm your phone number via a confirmation code that Facebook sends to you via text message.
Giving Facebook Messenger permission to read your contacts will let you add the contacts stored on your device as Messenger contacts if you want to.
It does seem more daunting when you're asked to give these permissions on Android because you'll be shown all of the possible permissions that Facebook Messenger needs at once without an explanation of what giving those permissions to the app will enable you to achieve. It's slightly different on iOS, because you'll be asked to give these permissions one at a time when you use various features available in the app. See also: How to stop Facebook automatically playing videos
"Almost all apps need permission to run on Android, and we use these permissions to run features in the app," writes Facebook in a blog post explaining why the Messenger app requests permission to access features on Android. "Keep in mind that Android controls the way the permissions are named, and the way they're named doesn't necessarily reflect the way the Messenger app and other apps use them."
So, while it is pretty annoying that Facebook wants us all to download the Messenger app (we all hate change, but we'll get used to it), don't let scaremongers put you off of downloading and using the app. All apps come with privacy concerns of one kind or another and Facebook Messenger is no different, but it's not going to spy on you and it's not going to send messages to your friends or call your family without you knowing. See also: How to deactivate or delete your Facebook account.