Gmail – How to get rid of MORE/LESS

I don't think you can tweak that but I see 2 partial solutions :

• Set up a filter. I think you could create a filter to mark as read all the emails that goes to the Spam folder.
• You can hide the Spam label. If you want it to be purged quickly I guess you don't go there often. Just go to Settings -> Labels and select Hide for the Spam system label. You may still be able to access the folder if you want by typing "in:Spam" as search criteria.

Just tell them that every e-mail is like a movie. The same movie can belong to more than one categories/genres like comedy, action, adventure, etc..