They all are already on WhatsApp though. All my phone contacts are WhatsApp contacts already (and have been before I added them).
If I need to interact with anyone who desires ultmost privacy I'm not idiot enough to ask for their phone number, and they'd be really out of their mind to share if that's the case.
But sure, I guess a cousin or smth might want to slap me in the face for "selling" data they already sold themselves years prior.