I would be happy if I went to add a photo to a text message and it said, "Allow Messages to access photos just this one time?" and I confirmed it. And then it turned off permission again after the message was composed.
What I don't like is when you get an app like "SuperPhotoStickers!"[1] which allegedly lets you take a picture, put stickers on it, and text it to a friend. Asks for permission to access texts all the time, and has a service that runs all the time, and later you find your phone has been sending photos and/or texts to a third party without you knowing about it. That is what I mean it is a broken permission system.
In a sane world you would be able to say "only access pictures taken with the App" and only access the text subsystem (SMS/MMS) only when "the App is open and the UI is on the screen in front of me."
[1] Example name, not a real app as far as I can tell.