Why not shamefully-flatten?

• It is long. I also find typing "shamefully" hard (no muscle memory).
• It is not intuitive: You cannot expect a user just to think of the word "shamefully" when they want it to be "flatten".
• Warning message is enough to discourage user from using it everywhere, "shamefully" is unnecessary.

Why flatten?

• It is reasonably short. I also find typing "flatten" way easier (as it is a more frequent word than "shamefully").
• It is intuitive. User may think of flatten immediately if they want a flat tree.

Suggestion

• Make flatten official option.
• Make shamefully-flatten an alias (that is going to be deprecated and removed in later versions).