In the import tool, we leverage import_id or constituent_id to control updates, why not also allow deletes? It is obviously up to the user to know how to first remove children records, etc. Global delete is not a straightforward option for normal deletes. For example, if we want to delete some custom fields (attributes). It deletes all of that particular custom field, not just the records in-use for that attribute type. That's ok for initial data loading but not a good system for general maintenances.