harry potter - Why didn't Dumbledore put the same spell on the books of the library in restricted area like the one on the marauders map?

In the books and movies, the marauder's map only reveals it's true information for someone who knows the password. If the books in the restricted area of the library are so dangerous and thus forbidden to young students, why Dumbledore did not put a spell on the books so that they will not show their contents unless the reader knows a specific password? The books claim that Dumbledore is one of the greatest wizards of the world: thus he probably knew, or could invent a spell like that.

Answer

I suspect that Dumbledore was not interested in making it impossible for students to access the forbidden books. If he really didn’t want them reading the books he could have just removed them from the library.

Indeed, even the books about Horcruxes which he did remove from the library were not placed under any extra security.

I believe this is because of Dumbledore’s educational philosophy. He believed that anyone who had enough skill and determination to do something had a right to do it. He put enough barriers to repel the average student, but if a student was able to get past the barriers then Dumbledore would have wanted the student to be able to read the books.

In fact, this is essentially what Hermione says in the beginning of Deathly Hallows when explaining how she got the Horcrux books:

Anyway, if he really didn’t want anyone to get at them, I’m sure he would have made it much harder to –

Harry seems to have recognized Dumbledore’s philosophy way back at the end of Philosopher’s Stone:

”No, it isn’t,” said Harry thoughtfully. “He’s a funny man, Dumbledore. I think he sort of wanted to give me a chance. I think he knows more or less everything that goes on here, you know. I reckon he had a pretty good idea we were going to try, and instead of stopping us, he just taught us enough to help. I don’t think it was an accident he let me find out how the mirror worked. It’s almost like he thought I had the right to face Voldemort if I could.

Interestingly, this character trait seems reminiscent (minus the killing at the end) of that which Dumbledore described in Voldemort at the end of Half-Blood Prince:

“I’m sorry, Harry; I should have said, he would not want to immediately kill the person who reached this island,” Dumbledore corrected himself. “He would want to keep them alive long enough to find out how they managed to penetrate so far through his defenses and, most importantly of all, why they were so intent upon emptying the basin. Do not forget that Lord Voldemort believes that he alone knows about his Horcruxes.