When importing a calendar into the Schedule tool, the "Remove" checkboxes are checked "on" as if the items should be removed prior to saving the import. All of the scheduled items are then imported.
I would set the default behavior to be unchecked prior to saving the import, and allow the user to check them "on" if they would like to remove the item.
I have attached a screenshot of the view just before the import is saved. The view is assuming an Outlook calendar import, but this also appears in Meeting Maker, too.