Until now all participants of group conversations in Messenger were equal, because every person had option to add anyone to this chat, but also every user had ability to delete anyone. This brought chaos to nearly all group chats, and Facebook decided to change it by the newest update for Messenger.
After new update group chats will work in the similar way to normal groups on Facebook. Every group chat will have its admin, and it will be the only person which will have ability to add or remove users from this conversation. Admin will be able to set Messenger to inform if someone will want to join the group chat, but admin will also have option to allow everyone join to this conversation without special permission. New version of Messenger is already available for download from App Store and Google Play Store.