You can actually sign up for a Messenger account independently of a Facebook account. However, this doesn't seem to be well supported. There is no way that I can tell to delete a Messenger-only account, or to remove contacts that were automatically uploaded from your phone.
I could trigger Messenger to log in to your shadow Facebook account. It will work mostly like a regular account with the exception you (mostly) can't interact with your friends. I reported it as a security bug last year. Somehow after I reported it, the app doesn't do it anymore. Fb security took another 6 months to discard it as a security bug.
I was too disappointed by how much they cared, so I don't even bother to make a blog post about that. I trust both Facebook and Facebook security less after working with them. I don't have a Messenger only account anymore (but then, my Messenger-only account was never deleted). But do they care? Probably not. Do I care? Maybe - but what can I do about it?
Here is the draft that I wrote up but didn't publish about the experience: https://docs.google.com/document/d/e/2PACX-1vSa-LjM5IzyTWJuD...
Obtain a visa to an EU country and/or sell your account to an EU citizen after May 25, so that they can either file a "right to be forgotten" request under the GDPR, or, generally, engage their "right of a Data Subject to withdraw consent" for personal data to be held against the account.
Either way this is by far one of the most exciting reasons I've encountered to still have my original citizenship!
Now, the downside is that small, local companies probably won't care about the GDPR. However, you buy soap (and everything else) from multinationals with European operations -- and crucially, bank accounts.
have searched online and cant find anything which leads me to believe that no one really does this.