Comment 7 for bug 1524293

Terminal-app requires a password when it's launched, so both the apps actually requires an authentication before accessing the SD card.

I'm not part of the Ubuntu File Manager team, what I'll write below is just an opinion as a Ubuntu Phone user.
Data in user's folders are as critical as data in a external storage. The same security policy should be used for these two "sources", and no password should be required when the user tries to access the SD card.
Other apps (e.g. camera-app, gallery-app) have a read/write SD card support, with no required password, since the version 1.0 of the confinement policies[1][2]

Thinking at a convergent Ubuntu device, whose owner may want to plug a USB pen drive, I believe this could be something strongly required.

I don't know where your report has been tracked, however I think this is something worth to be rediscussed. :)

[1] camera-app, gallery-app since version 1.0:

[2] music-app since 1.1: