Morality tends to become less necessary as one matures.
Are you using "morality" in some narrow technical sense, here? I ask because this statement seems so bizarrely false to me that it seems like you may have been saying something entirely different than my understanding of what you said.
I'm using a perfectly standard definition of morality. I can only assume you are using a different meaning of necessary.
Take, for example, 'crossing the road'. Look both ways, hold hands, etc. That is all presented using the mechanism for morality. This is necessary for most young children because their ability to reason out natural consequences and actually make responsible judgements is undeveloped. As an adult you don't need to to have a feeling when you cross the road that you may be transgressing on an absolute moral law. You take care because you kno...
[Update: and now there's a fifth discussion thread, which you should probably use in preference to this one. Later update: and a sixth -- in the discussion section, which is where these threads are living for now on. Also: tag for HP threads in the main section, and tag for HP threads in the discussion section.]
The third discussion thread is above 500 comments now, just like the others, so it's time for a new one. Predecessors: one, two, three. For anyone who's been on Mars and doesn't know what this is about: it's Eliezer's remarkable Harry Potter fanfic.
Spoiler warning and helpful suggestion (copied from those in the earlier threads):
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.