Is there a way to get the delete key to delete a file from a collection WITHOUT deleting the underlying file?
No, you do have to use the remove button at the top of the content panel for doing so
I never want to delete a file from my system when viewing it in a collection
You are right, it should not even be possible to delete the underlying file from a collection, this is a major flaw in the design of collections to my opinion. Deleting should only affect the alias in the collection not the underlying file itself.
You can set the delete key to either remove or reject (this is a choice you get after default install and hitting delete key) but that's it.
