Sure, they could potentially provide you with better service by spying on you 100% of the time. Would you accept that trade off?
I'm curious why is FB knowing every site I visit (or every site that has FB related analytics/ads/comments/like buttons/etc) embedded not creepy to you?
I get that when I visit the GAP or Target or Walmart there are security cameras. I get that they could use that info to decide how to better arrange the store. I get that they could even do something like notice what I'm looking at, put displays on the aisles and beam useful help/ads at me (I see you're looking at diapers, maybe you'd like some wet tissue on aisle 3)
But I'd find it creepy if their surveillance extended outside their store. I'd find it creepy if they could partner with every security camera with every other store. I look at shoes at Ecco an get a message from Walmart "We noticed you looking at shoes. We have lots of shoes on sale!" or "We saw you looked at jackets at Nordstroms. Your friend liked that green one you looked at".
Why is that any less creepy when I visit non-FB websites?