How can I accelerate the ripening of bananas? should not have been edited to expand it's scope, even if it to collapse two questions into one.
Edits aren't intended to change or expand the original intent of the question, not without the authors consent at least. Such edits should definitely be avoided after the question already has answers, which that one does. The expanded scope now makes all the current answers obsolete, which isn't a good thing.
Additionally, merging two questions into one which are asking opposite (although possibly related) related questions broadens the scope of that question. This might seem like a perfectly fine idea at first, but results in a few problems.
First, the broaden scope means each answer to be larger to be considered complete (aka address the whole question). This can result in useful information being lost if a user can answer part of the question, but not all of it.
The broaden scope can also make the answer harder to find, instead of easier. Consider the case where a user is only interested in one of the sub-questions of the merged question. In the event that each answer is complete (addresses every question in the merged question), they will need to search through a large answer in order to find the answer to their specific question.
Another possibility is that users will just post incomplete answers, which only address part of the merged question. In this case the user may not need to search through a larger answer to have their problem solved, but instead needs to search through several smaller answers to find the one answer which addresses their problem.
If the question were kept separate than the above problems go away. The user just looking how to ripen their bananas faster will come cross the relevant question and will quickly find the solution to their problem. The users who only know one answer, but not the other, will feel free to post their answer (resulting in no information being lost).