Sundance by Robert Silverberg

Sundance by Robert Silverberg (F&SF, June 1969) opens with this:

Today you liquidated about 50,000 Eaters in Sector A, and now you are spending an uneasy night. You and Herndon flew east at dawn with the green-gold sunrise at your backs and sprayed the neural pellets over a thousand hectares along the Forked River. You flew on into the prairie beyond the river, where the Eaters have already been wiped out, and had lunch sprawled on that thick, soft carpet of grass where the first settlement is expected to rise. Herndon picked some juiceflowers, and you enjoyed half an hour of mild hallucinations. Then, as you headed toward the copter to begin an afternoon of further pellet spraying, he said suddenly, “Tom, how would you feel about this if it turned out that the Eaters weren’t just animal pests? That they were people, say, with a language and rites and a history and all?”
You thought of how it had been for your own people.

We learn that the protagonist, Tom Two Ribbons (a Native American from a long line of unsuccessful men), is having doubts about the liquidation operation on this alien planet—he recalls the historical slaughter of bison and the Sioux on Earth. Later, we see he is in an open relationship with Ellen, another team member, and find out that he previously had a “personality reconstruct” after the collapse of a previous business (not his first failed venture, and he has also had two failed marriages).
The rest of the story sees Tom apparently witness ritual eating behaviour among the Eaters, and he later begins to believe they are intelligent. He withdraws into his research (to the concern of the other team-members), and eventually ends up out in the field, intoxicated on one of the local plants, dancing and, he thinks, communicating with the aliens:

We move in holy frenzy.
They sing, now, a blurred hymn of joy. They throw forth their arms, unclench their little claws. In unison they shift weight, left foot forward, right, left, right. Dance, brothers, dance, dance, dance! They press against me. Their flesh quivers; their smell is a sweet one. They gently thrust me across the field to a part of the meadow where the grass is deep and untrampled. Still dancing, we seek the oxygen-plants and find clumps of them beneath the grass, and they make their prayer and seize them with their awkward arms, separating the respiratory bodies from the photosynthetic spikes. The plants, in anguish, release floods of oxygen. My mind reels. I laugh and sing. The Eaters are nibbling the lemon-colored perforated globes, nibbling the stalks as well. They thrust their plants at me. It is a religious ceremony, I see. Take from us, eat with us, join with us, this is the body, this is the blood, take, eat, join. I bend forward and put a lemon-colored globe to my lips. I do not bite; I nibble, as they do, my teeth slicing away the skin of the globe. Juice spurts into my mouth while oxygen drenches my nostrils. The Eaters sing hosannas. I should be in full paint for this, paint of my forefathers, feathers, too, meeting their religion in the regalia of what should have been mine. Take, eat, join. The juice of the oxygen-plant flows in my veins. I embrace my brothers. I sing, and as my voice leaves my lips it becomes an arch that glistens like new steel, and I pitch my song lower, and the arch turns to tarnished silver. The Eaters crowd close. The scent of their bodies is fiery red to me. Their soft cries are puffs of steam. The sun is very warm; its rays are tiny jagged pings of puckered sound, close to the top of my range of hearing, plink! plink! plink! The thick grass hums to me, deep and rich, and the wind hurls points of flame along the prairie. I devour another oxygen-plant and then a third. My brothers laugh and shout. They tell me of their gods, the god of warmth, the god of food, the god of pleasure, the god of death, the god of holiness, the god of wrongness, and the others. They recite for me the names of their kings, and I hear their voices as splashes of green mold on the clean sheet of the sky. They instruct me in their holy rites. I must remember this, I tell myself, for when it is gone it will never come again. I continue to dance. They continue to dance. The color of the hills becomes rough and coarse, like abrasive gas. Take, eat, join. Dance. They are so gentle!
I hear the drone of the copter, suddenly.

Tom watches the helicopter drop pellets: the Eaters consume them and die, and their bodies dissolve into the ground. Then the helicopter picks him up and takes him back to base. We find out (spoiler) that the team hasn’t been killing the Eaters but that Tom has been experiencing a fantasy that is part of his psychological reconstruction, something designed to ameliorate his anger about the treatment of the Sioux.
After this Tom goes outside again and dances (he thinks) with generations of his people, and the story finishes with him switching between delusion and reality.
This is an interesting and generally absorbing piece about a man’s descent into madness, but it doesn’t quite work for a number of reasons: first, it is hard to accept that someone would still be so conflicted about what had happened to their forefathers—fathers or grandfathers perhaps, but once you get beyond that it is difficult to accept the idea of serious psychological problems (especially if you are so removed, i.e. on another planet, from that reality); second, it is ridiculous to think that making someone help with a massacre on another planet is going to help them come to terms with their own people’s trauma; third, you wouldn’t include someone with serious mental problems as part of a colonisation crew; and fourth, the shuttling between the first, second and third person has a distancing effect—a story about someone losing their mind would be more engaging if it was all written in the first person (and these point of view changes seem little more than a performative writing trick designed to make the story look like literature1).
Still, worth a look for the parts that are done well (the stream of consciousness delusions, etc.).
**+ (Average to Good). 5,700 words. Story link.

1. This story was nominated for that year’s Nebula Award (no surprise there: point of view changes, tick; near stream of consciousness writing, tick; indeterminate ending, tick; drug-taking, tick; Native American protagonist, tick) but was withdrawn in favour of Passengers (Orbit #4, 1968), which won.
Robert Silverberg has this to say about the story in his To the Dark Star: The Collected Stories of Robert Silverberg, Volume Two:

I was still living in rented quarters [in 1968]—in exile, as I thought of it then—but I had begun to adapt by now to the changed circumstances that the fire had brought, and I was working at something like the old pace. I was working at a new level of complexity, too—sure of myself and my technique, willing now to push the boundaries of the short-story form in any direction that seemed worth exploring. Stretching my technical skills was something that had concerned me as far back as 1955 and “The Songs of Summer”—but I had been a novice writer then, still a college undergraduate, and now I was in my thirties and approaching the height of my creative powers. So I did “Sundance” by way of producing a masterpiece in the original sense of the word—that is, a piece of work which is intended to demonstrate to a craftsman’s peers that he has ended his apprenticeship and has fully mastered the intricacies of his trade. Apparently I told Ed Ferman something about the story’s nature while I was working on it, and he must have reacted with some degree of apprehensiveness, because the letter I sent him on October 22, 1968 that accompanied the submitted manuscript says, “I quite understand your hesitation to commit yourself in advance to a story when you’ve been warned it’s experimental; but it’s not all that experimental….I felt that the only way I could properly convey the turmoil in the protagonist’s mind, the gradual dissolution of his hold on reality, was through the constant changing of persons and tenses; but as I read it through I think everything remains clear despite the frequent derailments of the reader.” And I added, “I don’t mean to say that I intend to disappear into the deep end of experimentalism. I don’t regard myself as a member of any ‘school’ of s-f, and don’t value obscurity for its own sake. Each story is a technical challenge unique unto itself, and I have to go where the spirit moves me. Sometimes it moves me to a relatively conventional strong-narrative item like ‘Fangs of the Trees,’ and sometimes to a relatively avant-garde item like this present ‘Sundance’; I’m just after the best way of telling my story, in each case.” Ferman responded on Nov 19 with: “You should do more of this sort of thing. ‘Sundance’ is by far the best of the three I’ve seen recently. It not only works; it works beautifully. The ending—with the trapdoor image and that last line—is perfectly consistent, and just fine.” He had only one suggestion: that I simplify the story’s structure a little, perhaps by eliminating the occasional use of second-person narrative. But I wasn’t about to do that. I replied with an explanation of why the story kept switching about between first person narrative, second person, third person present tense, and third person past tense. Each mode had its particular narrative significance in conveying the various reality-levels of the story, I told him: the first-person material was the protagonist’s interior monolog, progressively more incoherent and untrustworthy; the second-person passages provided objective description of his actions, showing his breakdown from the outside, but not so far outside as third person would be—and so forth. Ferman was convinced, and ran the story as is.

You could argue that if you cannot “properly convey the turmoil in the protagonist’s mind, the gradual dissolution of his hold on reality” in a first person story then you haven’t “fully mastered the intricacies of [your] trade”.
Perhaps I should run a poll to see who agrees with Ferman, and who with Silverberg.