What does that have to do with privacy? Just because the data is encrypted doesn't mean it can't be harvested by FB
WhatsApp is end to end encrypted. Facebook/WhatsApp can't see the contents of the messages. It's the best technology available at the moment - there are no non-toy systems that also scramble metadata.
WhatsApp claims to be end-to-end encrypted, but since it's closed-source, who knows what's actually going on.