Just take 'em off for good.
What happened to Freedom of Speech?
Tolerance is one of the main foundations of Freedom, because Freedom is not only about your own right, it's mostly about the rights of others -- and most of the time you will find yourself disagreeing with the rest of the world.
I, for once, completely disagree with your "just take 'em off for good" statement. Still, I believe in Freedom, so I must accept that this is your position, but I also absolutely and firmly believe that you have no right whatsoever as to limit or restrict ME or anybody else in what I think, believe, or in this case, might want to purchase or use.
Apple adding an "explicit" section is overdue. It should have been there from the very beginning, and Steve should never have said a childish thing like "obviously, no porn". This is only obvious for a prude American. It certainly is not obvious for the rest of the sexually liberated and more mature rest of the world.
Do I want that teenagers or children have access to it? Certainly not. But that is what we have an EXPLICIT rating for. I'm an adult, and I do not need Walt Disney or anybody else to tell me what I am allowed to watch.
And if Apple does not want to sell or provide such content, then they should allow other AppStores to provide that content.
Or will they also install web content filters in their next software updates so that Safari can no longer surf to Jenna Jameson's homepage? It would be the consequent next step, but how ridiculous would that be?