There's a huge difference between sharing what people have explicitly interacted with (making a comment, clicking "like") and sharing what people have passively viewed with no explicit action on their part.

With Facebook's f'ed up app ecosystem I've seen friends Like some pretty embarrassing stuff without realizing they had done so. And besides, the change has been recent, there has been a training period as people realized their Likes and comments were shared. I can't imagine how many millions of awkward embarrassing conversations have happened because these vampire companies don't care about their user's privacy.