Suppose someone offered to mow your lawn for free. Great offer, so you take them up on it. Turns out they're also using the access you give them to mine gold you didn't know was in your backyard. Whether or not you were addicted to their mowing services is irrelevant, they're stealing from you.
The problem with Facebook is that they're taking your attention and monetizing it. There's no serious argument against requiring them to disclose their actions - particularly who is buying your attention. It doesn't make any difference if you're addicted or a mere user of their product, they're still using your attention without telling you. They simply know more about science.