I don't think there is a simple answer as to who is right in this particular issue. Yes, I am repelled by people opposing science because of superstitious religious beliefs. But culture and cultural identity are real and crucial aspects of how people see themselves and give meaning to their lives. And the cultural importance of a location, a ritual, a style of dress, etc. to a person can be very real even when it is based on a belief in a non-existant God and a mythical creation story. I can fully understand and respect Hawaiians who see Mauna Kea as having extra special meaning to them, and accept that this special meaning needs to be acknowledged in decision making without seeing it as religion trumping science.
In my mind religion is irrelevant in this issue; it relates instead to the broader issue of recognizing the importance of someone's culture to them and trying to respect it, to work with it, whenever possible. Add to that the long history of mainland Americans destroying Hawaiian culture: pushing native Hawaiians from their land, imposed teaching of Christianity to their children by missionaries and belittling of their own culture, etc. I imagine one would become a bit touchy about anything that might resemble that today. And how it would feel if one's feelings and deep beliefs appeared to be meaningless and unimportant to those in government who supposedly were representing you?
That said, there are already many, many telescopes on this site (I've been there - very impressive). And I would very much like to see the 30 meter telescope built.
So what I hope for is a compromise. Frankly I think one should be possible because these compromises helped the other telescopes to be built.