Hi and welcome,
I never saw this problem. If both sides use Delta Chat you simply can leave the group. Similar to WhatsApp.
There also the problem if someone add your phone number to a group, every group member can see your phone number.
But of course if you not use Delta Chat, you can’t leave the group. So the “Remove from list” Link have to be added to every group message. Maybe inside the signature.
This way for Delta Chat users it would be invisible, but visible for regular mails.
And we need Broadcast lists as I mentioned before:
This feature could be used for e.g. newsletters as described in the article.