The way human remains are treated is entirely contextual. I don't think there are hard and fast rules. Any group whose history has been left unrecorded, been erased or includes a lot of persecution are likely to feel much more strongly about human remains that are directly relevent to them. I have native american indians in mind here but really its any group with a cultrual history similarly defined by loss. What if a mass grave of murdered african slaves was discovered? should they be treated as assets for the museum sector? What about the horrific story of the Tuam babies in Ireland? should we not bother with them?
I don't say human remains should always be treated as 'sacred' but the decision about that is highly nuanced and relates to the nature of the remains, their context, the circumstances of the death, the historical age... etc, etc.
Another example... here in Dorset a few years back a mass grave of vikings was discovered during the building of a road. They had all been publically beheaded very much in some sort of intentional legal or ceremonial setting. This happened roughly 700 years ago. The story of these young men is vaugue, and no one is exactly sure what motivated their deaths, but it was a gruesome act and a chilling fate. Now, those remains all went on display, and some still are. But there is still a recognition that the way they are described and their stories interpreted needs to be sensitive to the fact that these people are related to the national history of another country and another culture.
Reducing it to sentimentality is a rather serious underestimation of the importance of these things to people and the role human remains and their associated stories play in continually feeding into a shared sense of heritage, culture and identity.