When you want to remove an item from the playlist, you can right-click on a song
or go to the Edit menu, and choose "Delete".

The "Delete" moniker commonly denotes "remove this file from my computer".
Nautilus even differentiates between "Move to Trash" and "Delete", where
"Delete" irrevocably removes the file.

As such, it feels very weird to select a batch of my favourite mp3s in
rhythmbox, and choose to Delete them. At first, I had to mount my mp3 drive
read-only before choosing Delete in rhythmbox, just to make sure that it
wouldn't actually Delete my files.

I think it would be much better if "Remove" were used instead.