In the world in question, we have anatomically and psychologically normal humans living in a variety of societies. We also have trolls.
Trolls are a hominid species more closely related to humans than humans are to chimpanzees. Male trolls stand 2.4m/8ft tall, and females stand 2.1m/7ft tall on average, and have a heavy, muscular build, large canine teeth and furred skin. They are somewhat similar to an upright-walking Gigantopithecus (a large herbivorous extinct ape) but they are omnivorous, and prefer cold climates. They are a moderately intelligent, tool-using species with a language intelligible by humans and a primitive, somewhat human-like society. Like humans, Trolls have concealed estrus and copulate for social bonding to a degree somewhere between that of humans and that of bonobos.
It is possible for trolls and humans to interbreed, and despite the anatomical differences, the similarities between the two species anatomy and mating habits are sufficient that cross-breeding occurs fairly frequently (compared with the frequency of natural cross-breeding between other pairs of similar species under similar circumstances) where troll and human territories meet or where juvenile trolls are captured and kept by humans.
Keepers copulating with captive trolls is an important measure to keep a captive troll docile and cooperative, as it creates a social bond between captor and captive without which the captive troll is likely to be prone to violent outbursts.
Human children may be adopted by trolls if found unsupervised in or near troll territory.
Despite this, apparent compatibility between the two species, relationships between adult humans from a human society and free trolls are strained at best, since misunderstandings frequently lead to violence.
The 'half-troll' offspring of unions between trolls and humans are mid-way in intelligence, size and strength between humans and trolls. Most half-trolls are infertile, with perhaps 1 in 20 being fertile.
The phenomenon of truman offspring of the mating of a male troll with a female human have been common enough that such pregnancies have been studied by doctors on many occasions. Given the low birth weight and relatively small head of a truman infant, it has been scientifically demonstrated that truman pregnancies are less risky to human women than pure human pregnancies, and that there is an ongoing health benefit to the mother of a truman infant in that subsequent pregnancies, whether truman or human, are significantly less risky.
Conversely, humoll infants, the offspring of a male human and a female troll has a higher birth weight and a larger head than a troll infant. Given that female trolls have large pelvic openings and give birth relatively easily, humoll pregnancies and births have not been found to be significantly more risky to their troll mothers than troll pregnancies and births.
Half-trolls are not particularly well adapted to living in either human or troll societies. They are of lower intelligence than humans, and while physically strong, have a brutish appearance that is offputting to many humans. Conversely, while they are smarter than trolls, they are physically weaker and not as well adapted to living in trolls' preferred environment.
Male half-trolls appear to do best in human society, where they often find employment as manual labourers due to their strength and simple-mindedness, while in troll society, they are often injured or killed in dominance struggles with male trolls.
Female half-trolls appear to do best in troll society, where their greater intelligence allows them to quickly become proficient in the survival skills practised by trolls, and since the difference in appearance and physical abilities between female half-trolls and female trolls is not as great as the difference between male half-trolls and male trolls, they are more easily accepted. The appearance of a female half-troll is more offputting to most humans than it is to trolls.
Trolls are aware of the differences between themselves and humans, and while they don't generally attempt to extend their promiscuous sexual behavior to their human neighbors, they are sufficiently open-minded - or perhaps sufficiently innocent - that such relations are not automatically considered taboo or even unwelcome.
So... to the question:
While I believe that some human societies would disapprove of sexual relations between humans and trolls, or may consider them socially and legally taboo, I am unsure if such relations would be a universal taboo given the potential health benefits.
Is it reasonable to suppose that some human societies may consider sexual relations between humans and trolls to be natural and not particularly remarkable save for the fact that it is relatively uncommon, rather than automatically considering it to be a disgusting practice that should be eliminated or restricted to those of a lower class who must deal with trolls, and who are considered outcasts as a result?
If any societies would be tolerant of such relations, what sort of societies would they be?