What happens in The Turn of the Screw?

1/ I have written several blog posts about why the governess is an unreliable narrator and a liar, with an overactive imagination and perhaps a nervous breakdown.

2/ There is no evidence that Flora has ever seen anything. 
Take this passage from chapter 21 (near the end): 

“I wanted to be very just. “If you should wish still to wait, I would engage she shouldn’t see me.”
“No, no: it’s the place itself. She must leave it.” She held me a moment with heavy eyes, then brought out the rest. “Your idea’s the right one. I myself, miss—”
“Well?”
“I can’t stay.”
The look she gave me with it made me jump at possibilities. “You mean that, since yesterday, you have seen—?”
She shook her head with dignity. “I’ve heard—!”
“Heard?”
“From that child—horrors! There!” she sighed with tragic relief. “On my honor, miss, she says things—!” But at this evocation she broke down; she dropped, with a sudden sob, upon my sofa and, as I had seen her do before, gave way to all the grief of it.
It was quite in another manner that I, for my part, let myself go. “Oh, thank God!”
She sprang up again at this, drying her eyes with a groan. “‘Thank God’?”
“It so justifies me!”
“It does that, miss!”
I couldn’t have desired more emphasis, but I just hesitated. “She’s so horrible?”
I saw my colleague scarce knew how to put it. “Really shocking.”
“And about me?”
“About you, miss—since you must have it. It’s beyond everything, for a young lady; and I can’t think wherever she must have picked up—”
“The appalling language she applied to me? I can, then!” I broke in with a laugh that was doubtless significant enough.
It only, in truth, left my friend still more grave. “Well, perhaps I ought to also—since I’ve heard some of it before! Yet I can’t bear it,” the poor woman went on while, with the same movement, she glanced, on my dressing table, at the face of my watch. “But I must go back.”” 

That is no proof. The plausible explanation would be that Flora picked up “the appalling language” (probably swear words and obscenities) from Peter Quint (and perhaps Miss Jessel) when they were alive. It offers no proof that she is possessed, nor that she sees ghosts. 

3/ Regarding Miles being expelled from school: 

““Well—I said things.”
“Only that?”
“They thought it was enough!”
“To turn you out for?”
Never, truly, had a person “turned out” shown so little to explain it as this little person! He appeared to weigh my question, but in a manner quite detached and almost helpless. “Well, I suppose I oughtn’t.”
“But to whom did you say them?”
[…] “Was it to everyone?” I asked.
“No; it was only to—” But he gave a sick little headshake. “I don’t remember their names.”
“Were they then so many?”
“No—only a few. Those I liked.”
[…] “And did they repeat what you said?” I went on after a moment.
He was soon at some distance from me, still breathing hard and again with the air, though now without anger for it, of being confined against his will. Once more, as he had done before, he looked up at the dim day as if, of what had hitherto sustained him, nothing was left but an unspeakable anxiety. “Oh, yes,” he nevertheless replied—“they must have repeated them. To those they liked,” he added.
There was, somehow, less of it than I had expected; but I turned it over. “And these things came round—?”
“To the masters? Oh, yes!” he answered very simply. “But I didn’t know they’d tell.”
“The masters? They didn’t—they’ve never told. That’s why I ask you.”
He turned to me again his little beautiful fevered face. “Yes, it was too bad.”
“Too bad?”
“What I suppose I sometimes said. To write home.”” (Ch.24) 

He gets expelled from saying things. What things? Either “appalling language”—swear words and obscenities inappropriate for his age, or about what Quint (and Miss Jessel) did to him and Flora. 
I mean, I do think there’s some kind of sexual abuse. 
There is evil in the book, but not of the supernatural. 

4/ Let’s examine the passage that describes Quint’s death: 

“… Peter Quint was found, by a laborer going to early work, stone dead on the road from the village: a catastrophe explained—superficially at least—by a visible wound to his head; such a wound as might have been produced—and as, on the final evidence, had been—by a fatal slip, in the dark and after leaving the public house, on the steepish icy slope, a wrong path altogether, at the bottom of which he lay. The icy slope, the turn mistaken at night and in liquor, accounted for much—practically, in the end and after the inquest and boundless chatter, for everything; but there had been matters in his life—strange passages and perils, secret disorders, vices more than suspected—that would have accounted for a good deal more.” (Ch.6) 

Maybe it isn’t an accident? Maybe he’s killed? 

I’m reading the Norton edition, which includes criticisms and analyses. Let’s see what critics have to say.