This is an extraordinarily generous and almost child-like perspective on business.
You're correct that McDonald's doesn't hold a gun to your head and make you fat. That doesn't mean McDonald's plays no role in making you fat.
As with everything, there are many compounding factors that contribute to an outcome. If McDonald's only sold, say, kale salads, would you gain the same amount of weight? No, right? So therefore, McDonald's must have some hand in making people fat.
Again, I circle back to Tobacco because nicotine is plainly addictive, but do you truly believe that the Tobacco industry had nothing to do with societal smoking? That's rhetorical, I know you don't believe that because it's so obviously incorrect.
While social media does not contain nicotine, how confident are you that it is not addictive? For me, I'm not very confident.
> but wouldn’t they have fallen for some other thing if not Facebook? There is lots of shit out there on the radio, TV, books, cults
And instead of smoking, could those people have just gotten addicted to sunflower seeds? Well, why didn't they?
Because the nature of the medium and product matters. Social media is always immediately available. It features bright colors. And it's extraordinarily fast-paced. Compare that to a book - and it should be obvious why people are addicted to Facebook and not To Kill a Mockingbird.