It's true that Facebook almost certainly tracks users through the like button, but that is different than what is being talked about here. When Facebook tracks that you read a webpage through a like button, they do not display it in your friends feeds.
While many people reasonably aren't comfortable with Facebook knowing where you're going all the time, it is a very different thing than Facebook sharing that knowledge with all of your Facebook friends.
That feature, the one the original article is talking about, requires you to specifically opt-in before the "Bob read an article about sexual dysfunction" starts showing up in everyone else's news feeds.
While many people reasonably aren't comfortable with Facebook knowing where you're going all the time, it is a very different thing than Facebook sharing that knowledge with all of your Facebook friends.
That feature, the one the original article is talking about, requires you to specifically opt-in before the "Bob read an article about sexual dysfunction" starts showing up in everyone else's news feeds.