This article specifically talks about sex workers using whatsapp and the fact that because of meta data sharing, IF a warrant comes from the government to find users associated with a certain group (such as sex workers groups) on Facebook, it indirectly brings whatsapp users into that group as well through indirect means.
Interesting issue yet so many "if"s. The reality is that Facebook needs to make money from whatsapp at some point. If keeping end to end message encryption is important, then they are left with three equally bad options:
# Charge for the service (whatsapp will lose 90% of its userbase in a month)
# Show generic ads (worse value than even TV ads, because at least TV ads know a little bit about the viewers of a certain show but whatsapp has no idea)
The big issue I have with this is that facebook can already do this, IF a warrant comes from the government.
The issue about being careful about using those metadata for friends/"you could know" (which was always terrible for me) and related functionality is legit though. They should give the user the option of opting out (ex: I don't want you to show my FB profile to people I only have in whatsapp/instagram). Even better, they should allow for opting in and opt out everyone by default.
# Charge for the service (whatsapp will lose 90% of its userbase in a month)
# Show generic ads (worse value than even TV ads, because at least TV ads know a little bit about the viewers of a certain show but whatsapp has no idea)
# Figure out a way to deliver targeted ads.