An option must be provided to hide the preview widget that is displayed as the last column when the index has no children. I've looked everywhere on the internet and umpteen number of users didn't want the preview widget to be added as the last column all the time.

Not everybody want to show the preview widget and it's not suitable for all use cases. See the related threads below

http://stackoverflow.com/questions/33370223/qcolumnview-is-rolled-to-empty-column
http://stackoverflow.com/questions/38834428/qt-is-it-possible-to-turn-off-previewwidget-in-qcolumnview
http://stackoverflow.com/questions/3419185/is-it-possible-to-remove-the-preview-widget-from-a-qt-qcolumnview
http://www.qtcentre.org/threads/59917-Columnview-removing-final-column
http://www.qtcentre.org/threads/22566-How-to-turn-off-this-annoying-feature-of-QColumnView