“For a real in-depth analysis of this, read Harry Potter and the Methods of Rationality.”
I almost loved this one. The first ten chapters or so were fantastic. But he took it too far and it felt like it got very boring and dry very quickly (which is a shme, because he can be hilarious when he wants to be…).
While I can’t pretend to be nearly as good at this stuff as all of you folks, a possible explanation of the Marauder’s Map thing: the map could obviously tell who was reading it- we know that from when it insulted Snape. (Of course, it’s possible that this was specifically written for Snape, but let’s pretend it wasn’t, because I want to pretend to be smart here.) It’s possible that the map could tell that Fred and George were the “right sort” and therefore it trusted them and somehow gave them the ability to access it. I can think of two ways- either it wrote it on the parchment (the way stuff was written on it for Snape) or the phrase “I solemnly swear I am up to no good” wasn’t even the original password- it was something that Fred or George happened to say that the map happened to like and trust and that it opened up to them for, and Fred and George, being intelligent, figured out that that was a kind of password for them. The people to whom the twins gave the map could obviously be trusted- not to mention that one of them is the son of one of the people who created the map in the first place.