Misleading title: you elect what to want to share.
You have to “opt in”.
Netflix is unneccessary, Facebook is dangerous and stupid.
It's totally unpredictable, a former friend liked a pic of mine on Facebook, I didn't think you could do that, and I set my updates to friends only.
Facebook is like a Nazi informant and your the Jew it's after.
I don't have accounts on either of these (well, real-name one, anyway), but it is extremely easy to opt-in to these things by mistake, since they will ask you at different times, in different contexts, and hope that you flub up just once.
Also, even if you keep segregated email accounts, it is easy to use the wrong one just once in conjunction with the social account and have it linked against your wishes and maybe even unbeknownst to you. Even if you remove the association later, it is forever retained in the archive records.
It is really, really difficult to keep their tentacles out of your stuff over time.
The article also says that Netflix customers will have the option to turn off the sharing feature so the information is contradictory. Like with Facebook and its endless changing of privacy rules and changes, any customer should approach something like this with caution and read the fine print carefully and check account settings frequently.