You can quickly build relational graphs if you know which devices contain media that shares hashes. Sure, theoretical danger and not how this is implemented as

You can quickly build relational graphs if you know which devices contain media that shares hashes. Sure, theoretical danger and not how this is implemented as hashes are just compared locally. This is different from accessing peoples contact lists they upload anyway because you want to group people in information bubbles that not necessarily correspond with real life contacts. This is very valuable info, isn't Google trying something similar?