Consider that Whatsapp has no information about the content of any messages sent between users, so any content within the messages that are sent cannot be harvested to generate any kind of targeted advertising, the *only* thing that they have are names and phone numbers, and who is sending messages to whom, with no basis for understanding why beyond anything that might have been communicated out of band directly to Whatsapp. So since Whatsapp has no information about its users that can be used to actually generate any kind of "improved advertising experience" for its users, the assumption that this is what they actually are trying to do cannot possibly be correct.
Do you not remember the fight against the NSA's bulk metadata collection program?
Metadata is very powerful for mass surveillance with the facade of improving advertising experiences.
I don't care whether it's a sovereign government or a corporation. Mass surveillance is wrong.