That whole "books and movies don't deny you content" argument is a bit fallacious imo. If you don't understand the contents or themes of a book/movie, it will not explain itself to you past what is already in it. If that's not enough for you, tough luck.
Some games allow you to jump to later levels in order to see all the content, but if you do that, you probably won't enjoy it very much. Same with skipping certain parts of books or movies you don't understand. Yeah, you'll see all the content it has to offer, but you probably won't enjoy it, if you can't understand it.
But most importantly, games are not movies, are not books, are not games. A game is a set of challenges you have to overcome within certain rulesets. If you skip that, you're not playing the game anymore and you are not enjoying it as a game anymore, even if you might still enjoy it.
On Dark Souls:
I think the fear here is based on the "give an inch, take a mile" principle. Right now, adding an easy mode seems like a no brainer, since the game is designed around the normal, challenging mode. It would, like you said, allow less skilled players to enjoy the game too by making enemies weaker/the pc stronger or whatever.
But, come the next game, the designers might design it the other way around to reach a broader audience. By that I mean designing the game around the easy mode and just giving the players looking for more challenge a "normal" mode that bloats up the HP and damage your enemies do, like it is in most games nowadays.
This is not an unfounded fear, since it is pretty much what happened in every other genre. First, some things are "streamlined" away or can be activated/deactivated in the options/through selecting a certain difficulty to broaden the base. But the games are still designed with the core audience in mind. Then, when people see all that money coming in from the new players, they start catering to them more and more, to make more and more money.
Gradually, the focus shifts and the core audience gets the shaft.