Er, isn't that how onedrive works? It's not a "tin foil hat" move to point out that that's exactly what does happen to users who aren't paying attention and opting out, and it's equally valid to extrapolate that they might continue similar behaviors with new features.

No, OneDrive doesn't upload all data from all attached drives.

You're right, it only started uploading people's most important data without clear and deliberate setup, not all their data.

That's more than enough to make these worries not tinfoil hat.