We added the ckbk links as a service for members who subscribe to both services. And also to give our members a huge new resource (currently 77,000) of free online recipes - you can access 3 recipes a month with a free ckbk membership. It is not advertising (we don't get paid by ckbk).
I'm not sure what you mean by deleting all recipes under a bookmark - you haven't added the ckbk books to your Bookshelf so you don't have the bookmark on your Bookshelf. The ckbk logos you see are links to the book and recipe on ckbk. You cannot delete individual recipes from a book on your Bookshelf.
For any member who doesn't want to to see the ckbk recipes in the Library Online Recipes, you can switch a toggle on your Account page, accessed from the drop-down menu under your username at top right (or under the menu on a phone).