Keep in mind that not all of us who want to screenshot or save your photos are trying to steal them to distribute elsewhere. Some of us just like something we see, and want to save a local copy for ourselves because the Internet is ephemeral and the things we find and love there won't be around forever.
I've saved countless photos, archives of web pages and so on because they touched me in some way and I never want to lose the ability to see them. We are slowly losing that as companies put in technological measures to keep us from saving content; look at the hacks necessary to save from Instagram and Snapchat.
Agreed..sometimes it just makes cool wallpaper. I do respect copyrighted material though so I can see both sides. Not a fan of this being added to apps if this removes a function of my phone. I would delete the app if a dev added this to an app.