I have first posted this question on Super User. Since I tagged it with Android (as I use WhatsApp on Android) it got migrated to Android Enthusiasts. There one decided that it was not on-topic for that site and got closed. This question does address the technical side of uploading only a partial address book, but it mainly focuses on the legal perspective. So perhaps it is on-topic here.
Address Book. You provide us the phone numbers of WhatsApp users and your other contacts in your mobile phone address book on a regular basis. You confirm you are authorized to provide us such numbers to allow us to provide our Services.
So in principle I would have to send a message to each and every one of my contacts in order to ask. And while I am at it, I would actually also ask for Telegram, Hangouts, Wire, Skype, Duo, Signal; perhaps just a general authorization would be the easiest.
Then I get back a bunch of messages which I archive somewhere securely in care somebody sues me about it. Then I can prove that they gave me permission to upload their contact details. This is just tedious and a lot of work, but technically it can be done.
What do I do about the people who do not agree? Android 6.0 on my phone does not seem to allow to give only selected contacts to WhatsApp. This means that I would have to delete the number on my phone which sounds utterly inconvenient. My contacts are stored in my Google account. Should I have asked my contacts for that already?
Is there anything I can actually do about this? I think my options are the following:
Continue to use WhatsApp (like virtually everyone else) and ignore that I could potentially be sued by somebody who would not consent to his contact information being uploaded.
As I am a German citizen living in Germany, I am not sure where I would be sued, actually. WhatsApp has no department in Germany, so the US law covers my relationship with WhatsApp. Can another German citizen sue with under US law in Germany? Can only US citizens sue me, would I have to fly to the US? All in all it seems like a non-issue in personal life.
Delete the WhatsApp account (if possible) and not use the service any more. In principle I would have to get rid of all the other messaging apps as well. I couldn't store my contact list in my Google account then either, right? That is also sharing the data with other people.
Attempt to ask every one of my 532 contacts whether it is okay to upload their phone number. Otherwise delete the phone number or the whole contact from my address book. Keep track of these numbers in a paper notebook at home (in a safe).
My actual question: Is the third option actually possible? And what could happen if I stick with option one?