As much as I love going back and editing things, I think this is a good solution. On Reddit it's even a recurring game to challenge people to ask questions and then edit them to make the answer look bad.
I'm not convinced this argument holds for the time window limiting deletion of comments.
That helps, but if you forget to do it you can end up getting hosed. Also, it's confusing to the reader if the quote is no longer present in the comment being quoted.
I'm not convinced this argument holds for the time window limiting deletion of comments.