If I export a database collection to a CSV and then import it, each row gets duplicated. If I started with 34 rows, I now have 68 rows. Titles are no longer unique. I'm sure most of us would rather have an import option that replaces rows that have the same title. Import would then feel more like a restore.
This feature is especially needed if another collection has references to this table. Without it, it's easy to end up with broken references by deleting the wrong duplicate.