If you have previously recommended this thread, you should see a tick / check mark on the recommend button. Click the tick to undo the recommendation (the tick may appear to change to a cross as you do this.) If you added a comment with your recommendation, you will need to delete that from your facebook wall separately.
Now all we need is variations on the deleted post messages: e.g. post deleted for goading post deleted for personal attack post deleted for outrageous -ist comment post deleted for replying to/copying deleted post