Does it annoy anyone else when friends of friends/randoms to you, join your fireteam? If they're invited, fair enough. Or if your friend let's you know he has more people with him. It winds me up when people just decide to join and I hate kicking people, but in this scenario, I'll make an exception, lol. If I see a friend is doing a raid and there's 5 of them, I'll message to see if they need a 6th. What if they are going for flawless raider? What if someone got disconnected? I just think it's polite to ask and not assume you are welcome to join, lol.