Regarding “Reddit users have no control over the mirror”. I’d argue that they do have a way to delete the content from Lemmy and it’s quite simple. Any user that has been mirrored by alien.top needs to do the following:
When Google and company do “opt-out” features that people are forced into using unless they manually opt-out (usually with long and convoluted procedures that aren’t front and centre in the docs), they are (rightly) excoriated for it.
Thankfully you don’t have long and convoluted procedures to opt out…
Sign up via the portal to take over the bot account.
Login to the instance using the password provided.
Delete all their posts.
… Oops.
Rethink this if you don’t want really serious backlash. This is almost the textbook case of how not to do features.