I thought with Android Marshmallow and iOS you can deny access to contacts. I guess if you're not on Marshmallow or higher, you're not going to get this benefit
A lot of apps these days will not run unless they get access to the data they request. What I would like to see is android having the ability to give empty sets of information if so chosen instead of denying access, or to compartmentalize applications access to shared resources more.
You can't get what's app to do anything if you don't grant it access to your contacts. I ended up creating a new user profile on my phone based on a new Gmail account just to run what's app...