> Instagram provides that illusion by not injecting opinionated content into your feed (The most obvious example: you aren't seeing injected news stories in your Instagram feed, generally its only ads and people you follow, and the ads are marked)

What Facebook content do you consider "injected"? AFAIK, the only things in feed are:

1) Posts, events, shares, etc from people or pages that you follow

2) Posts that your friends have interacted with (liked, commented on, etc)

3) Ads that are marked as "promoted"