With a double edged sword - they also removed the organic engagement you previously would have gotten

> You can buy interactions

You're describing advertisment in general. Same with FB. If I throw enough money at a posting ad, I will gain interactions.

You're missing the point. There's a difference between buying an ad, something that's clearly marked as an ad and inserted as an ad, vs having your normal posts appear organic but still getting put in front of more people.

Or, it's mainly the opposite. If you don't pay, you no longer get the organic, not even from your own followers.

On FB ads are not very clearly marked - the "sponsored" in grey lettering is not very noticeable.

They also promote anything that gets engagement which leads to showing people a lot of very nasty stuff.