I'm not sure what you mean. If you don't share a photo when you upload it, you can share it any time later. (In particular, that's how auto-upload works.) If you share it, and then you delete the post where it's shared, it goes back to not-shared. That seems pretty straightforward.

It doesn't seem like a surprising UI to follow an upload with a share when you're sending photos to a social network. I'm not even sure Facebook gives you that choice. The two actions don't have to be associated, but they certainly need to be associated when you consider that folks usually upload photos to share them.

I don't think G+ Photos has been advertised as a "persistent store you control". It's a social network that has an auto-upload feature to make it easier to share images and backup shots taken on your phone. "Hosting your own" is not going to be a substitute for 95% of real-world users.