Is authentication necessary for Facebook and Instagram's realtime webhooks/subscription APIs?

Based on the way the docs are worded, it seems as if each Instagram handle or Facebook user, that I want to obtain push-notifications for, has to manually authenticate my app. Is there no way to do it without that? I'm not looking to fetch any private information; only publicly available information.

In contrast, Twitter's Firehose API - as well as YouTube's push notifications - don't need any authentication from users. You just specify what handles or channels you want updates for, and you get them in real-time. Then why would Facebook or Instagram require it? It seems impractical; if a user, who isn't on Instagram or Facebook, simply wants to use my service to aggregate posts from his or her favourite sportspersons (or whatever), why would I have to request authentication from those handles?

Solution

Based on my conversation on this thread on the Facebook Developers Group:

If you're accessing an individual user's data (even public), you need them to authenticate.
If you're accessing a page's public data, you don't need any authentication beyond your API keys etc.