I just mentioned this problem in the private Messenger beta chat we had with part of the development team. They said basically if things like that are enough suggested, they see what they can do about it. In other words, they never knew it was such a big issue with many people as it hasn't been reported that much before.
So I'd suggest to suggest to MS to add a
"always ask for confirmation before I'm added to a group convo"-option.
/ 
