I'd say there really needs to be the ability turn delete content on or off, and it needs to be a separate setting for both recorded shows and imported content. I'd suggest putting the setting under the import content menu.
Like others have said, I would never use Channels DVR to delete the imported content, as that is where all content I want to keep perpetually is stored. I would actually prefer the imported content to be under a different menu item, instead of being poured in with all the recordings. I view those two items as completely different things, so it only confuses things to pour them into the same bucket. Separating them would further help prevent errant deletion, because it enforces the fact they are two completely different sources.
It's because of previous errant deletions that I removed all imported content from Channels DVR, and am not likely bring it back in until this deletion is fully resolved with the ability to turn the setting off separately for both imported and recorded items.
The option to put the entire imported library as read-only is not really an option as it would require quite a bit extra work for automated naming/moving/tagging processes. Besides, it would seem like a drastic step when the real solution appears to be a fairly simple one. Unless you are targeting superusers as your primary user base, it wouldn't be a good idea to require people use advanced file management techniques to remedy issues such as this.
I really do see Channels DVR as my go-to app for entertainment, and it's getting better all the time. I appreciate all the work you've done and continue to do in development. I've been with you from the start and you all have exceeded my wildest dreams - and you are still hard at work. I'm sure this issue will be handled in a way that helps us all protect our content, and then this really will be the one stop app for entertainment!
Thanks!
Chief