Sounds like the best that can be hoped for, though I understand the continuing mistrust. They have decades worth of reasons to be skeptical even if the majority is okay with it.I think these discussions are healthy but some of the nuance in the current TMT situation is not being communicated.
The TMT project has been in the works for over 15 years, but Mauna Kea was selected as the site back in 2009. Since that time, it has undergone a rigorous environmental impact study and it worked extensively to accommodate the concerns of the local community. For example, the TMT construction site is not located on the exact summit of Mauna Kea, but at a position over a mile away to the NNE. Archeological studies have shown no previous cultural activity or burials at this location, and no species will be impacted by TMT's presence there. Also, the telescope enclosure will not be visible from lower elevations at that location. I believe it will also be painted to blend into the surroundings.
Mauna Kea is arguably the best astronomical observing location on Earth. It is a false equivalence to say it can be just moved to the Canary Islands. Moving TMT there would mean a lesser instrument, one that may not even warrant construction given the cost. Indeed, the weather on La Palma is poorer than on Mauna Kea, meaning fewer clear nights and worse image quality, and the lower elevation of La Palma means some projects, particularly studying exoplanets in the mid-infrared, will not be possible. Management of Mauna Kea has improved dramatically over the years that observatories have been there, with great deference and respect to native Hawaiian concerns. For example, all construction activities are accompanied by further activities to return any disturbed land to its natural state. This includes the decommissioning of telescopes, even TMT, in the future. Note also that the observatories are on public land, and their presence has not restricted access to the summit area to the public.
The native Hawaiians who are currently protesting have a right to do so. The protestors who were arrested were cited for illegally blocking a public road, not because they were protesting. The arrests were done on the third day of protest, after they were asked repeatedly to not block the road. Those who were arrested, especially the elders, were handled very respectfully and soon released - there was no violence. The arresting officers were from local police. The National Guard was called up, but not to interact with the protestors but instead to provide logistical support to the local police effort.
Though Hawaii has had an unfortunate history where native concerns have not been considered by those in power (to put it mildly), the TMT project has tried to work differently. It recognized from the very beginning that native community engagement is important. For example, TMT will be funding the THINK program, providing up to $1M / year to support education within the local community. In addition, it has begun a Workforce Pipeline Program to steer Hawaiians into science and technology jobs. I believe it is also the aim of the project to staff the facility with locals. The project will be an economic benefit to the local community.
TMT followed the rules laid down by the State of Hawaii, including affirmation of its building permit by the Hawaii Supreme Court. It has not acted unilaterally in its development without regard to native concerns. Hopefully, the project will continue to engage with the protestors to communicate its net benefits to Hawaii and its native community. The project and its international backers, however, can only do so much. Ultimately, it will be up to Hawaiians themselves to decide if the project will go forward there.
For further details on the TMT project, see http://www.maunakeaandtmt.org.
If a popular vote of some kind is needed to address these concerns and to let everyone be heard, they should do so.