Sometimes destructive edits are not possible in the Sample Edit window, which you know is the case when items in the Functions and Factory menus are dimmed.
This occurs when you are working with audio files for which you have read-only access. This might happen, for example, if you save a project to a network volume and then try to edit audio. It can also happen when the opened audio file is written in a compressed file format, such as AAC (".m4p"). In versions of Logic prior to 7.2, you would have access to the menu items, but an alert message indicating lack of write access would appear.