These nutty outlier things are a part of what defines D&D fantasy -- the kitchen-sinkiness of it, the free-for-all nature of it-- and separates it from a hypothetical RPG that's more focused on strict genre-emulation.
This is where your argument and many other people screw up, and probably shouldn't be playing D&D or many other games if they cannot understand that just because some secondary product has some strange crap in it, does not make it a part of the core that does define D&D.
By your logic, since I have played a game that had an adventure based fully around rpae and slavery, then D&D must be a game about rape and slavery since there is a single instance of it in there right?
No. Your are wrong. A VCR is not a toaster, just because you can stick a slice of bread into it.
Learn to use the language properly. When talking about the core, with the exception of 4th edition and its stupidity; you are discounting all things other than the minimal required to play the game.
AD&D that was PHB, MM, DMG; and arguably the MM wasn't really needed.
3rd is similar, and older editions needed only 2 books.
Just because all those settings existed in AD&D does not make that what D&D is, and just because Blackmoor and Greyhawk had a single instance of random crap, does not mean that is what it is.
Your core is the minimum required to play, no matter how WotC wants to brainwash people into thinking with 4th edition.
So please use the language correctly, and not fall prey to marketing scams and advertisement hype in a discussion because you were fooled by them.
So is D&D a game about rape an slavery, just because one adventure exists about it, like you try to define D&D by that one adventure written about aliens; or is D&D what is in the core, and the rest is just added crap like more of the supplemental material?
This is where the whole confusion exists in people trying to claim D&D is some sort of throw everything in including the kitchen sink, because it does allow it, but that isn't D&D.
D&D is what you buy at the store. You won't find your stupid lasers and six-shooters in the starter set, and the core books even tell you an arequebus is extremely rare IF, notice the BIG IF, you want to use them for your time setting, but are NOT standards for use in D&D.
So stop trying to confuse people with your misunderstandings, and other people's bold faced lies.
The adventure I was in about rape and slavery is no more a part of what defines D&D that your outlier things.
Read and learn the core. Just because you can add crap to the core, doesn't mean you should.
D&D was considered a "system" because there was no other name for it prior to 2000.
Yes there was a name for it. GAME.
You want a system try
GURPS - Generic Universal RolePlaying System