I'm that dad, I'm afraid. The fact that the app demands full access to all contacts on your phone to work nicely is just evil. And people happily give meta the full contact details of their family, doctor, bank, boss etc. - without those people's permission. The value in the harvested social graph is huge
Fair enough, but my Dad sends normal texts because he thinks WhatsApp is too complicated to use, or just because he forgets he has it, not for any security concerns... So you're not quite the same!