Many apps will refuse to work if you don't allow access to your contacts, so people just give in and allow it.

Google is the biggest abuser in this area just grabbing all your contacts and linking them to your Google account once you add any Google account (like Gmail or Youtube) to your Android device.

>Are people really that stupid to give some mobile app company access to their contact list?

Almost every social media startup in the last 15 years was bootstrapped this way.

Afaik WhatsApp (on Android at least) requires you giving access to your contacts. So roughly speaking a huge chunk, probably the majority, of smartphone users shared their contact list to at least one company, which strictly speaking might not even be legal in many cases.

After all that's how WhatsApp populates its contact list, it looks which users have each other's phone numbers. That way it doesn't need a user login and friend/contact requests, but in return you give up your privacy.

Everyone doesn't have to. If one person with your number gives up their contact list, they have yours. I'd guess about 10-12% of the populace would have to cooperate.

That was what made Clubhouse so famous:

"After registering, the clubhouse app asks for access to your address book. This must be granted if you want to invite friends."

I keep no contacts on my phone and gladly give that info away. I'm surprised people don't use multiple phones for privacy.

Based on the popularity of WhatsApp, yes most people don't give it a second thought.

Yes, constantly.

Yes.