The (real?) reason why Harry is raised by the Dursleys is mentioned in DH:
(Snape) “I have spied for you and lied for you, put myself in mortal danger for you. Everything was supposed to be to keep Lily Potter’s son safe. Now you tell me you have been raising him like a pig for slaughter —”
“But this is touching, Severus,” said Dumbledore seriously. (DH)
Note that Dumbledore doesn't deny Snape's observation, Dumbledore wanted Harry to be raised like a pig for slaughter. The Dursley's abuse is instrumental to this: They make him have no sense of self worth, believe that everything bad that happens is his fault and responsibility. As a result of his upbringing, he has no problems walking to his death, it seems natural to him.
This is not about keeping Harry humble, it is psychical abuse.
Dumbledore says that Harry has to die because of his scar. Would Dumbledore want to remove Harry's scar? No.
(Dumbledore) “Even if I could, I wouldn’t. Scars can come in handy.”
Note that Dumbledore knew how Harry's time with the Dursleys would be, even before he placed him there:
“You had suffered. I knew you would when I left you on your aunt and uncle’s doorstep. I knew I was condemning you to ten dark and difficult years.” (OotP)
But he also had Harry's misery confirmed by Mrs. Figg:
“Dumbledore’s orders. I was to keep an eye on you but not say anything, you were too young. I’m sorry I gave you such a miserable time, but the Dursleys would never have let you come if they’d thought you enjoyed it.” (OotP)
So Mrs. Figg and by extension Dumbledore were aware that the Dursleys were not indifferent towards Harry, they actively wanted Harry to be miserable.
It would have been easy for Dumbledore to make sure Harry is treated decently, but he didn't want that. Notice how just the address on the letter leads to Harry having his own room:
“Vernon,” Aunt Petunia was saying in a quivering voice, “look at the address — how could they possibly know where he sleeps? You don’t think they’re watching the house?”
“Er — yes, Harry — about this cupboard. Your aunt and I have been thinking … you’re really getting a bit big for it … we think it might be nice if you moved into Dudley’s second bedroom.” (PS)
On the other hand, we don't know what kind of protection Harry may or may not have from living with the Dursleys. He is obviously not protected against the Dursleys. But he is also not protected against the Dementors in OotP. Maybe Harry is protected while inside the house, but he doesn't spend his whole time inside.