I WAS for the rail, but always with the caveat "if it was done right". I lived in Seattle when they were going through the proposal and development phase for their rail. I moved before it got started, but it is my understanding that it's doing well. However, that's because downtown Seattle has a pretty linear arrangement with two popular recreation type areas north and south of the city. Then there's UW and other "areas of interest" that are pretty much linear. That's NOT how Hawaii is layed out.
Then there are those that seem to fall back on how rail is successful elsewhere, like BART and the L. Look at the way those cities are arranged and logistics on how people get around. In Chicago, there are many areas where people just don't drive, so the train is convenient. You also have to have existing infrastructure to get people to the stations, like local buses, park and rides, etc. I didn't see good plans for those.
And you can't look at mass transit in places like Japan, China, etc and ask why can't it work here. . . are you kidding me? Totally different context. Yes, Hawaii may eventually end up like those cities, but they are worlds apart.
That's all without all of the political, corruption, etc BS that went on.
Yes, as the path gets past the airport, environmental and archaeological issues with be much more than what has already been completed.