Comment by stephen_g

I think it's assumed that you are going to post any photos you take when you use Instagram - as the app doesn't actually save photos to your phone unless you post it (or if the upload fails).

I would understand the concern if it acted like a camera app - ie, you take a photo, it's saved to your phone's photostream, and afterwards you can choose to hit upload, but since you can't use it in that way (it's either post it or the photo is gone) I don't really see a problem.