Well, call me a snob. Glue shouldn't be used for a lot of our stitching because it often can ruin it in a short period of time.
That being said, glue has always been used to affix stitching to objects. One has only to look at those beautiful stumpwork boxes that came out of the 17th century. And gluing down fabric to all types of boxes is also centuries old.
What most of us mean when we say, "Don't use glue" is a caution, expecially to newcomers. We can't possibly know the circumstances and where someone will glue something. Or what kind of glue they are using. So, it makes common sense. Just like, "Don't use masking tape." Now, I've used masking tape, but I know what I'm doing. I leave plenty of border.
Anyway, I think you get my drift. It's a courtesy to tell newcomers not to use glue. And everytime the conversation comes up, and there are the naysayers, there are always those who will say, "I glue. If you glue, be careful, etc."
Dianne