At-grade trains are nowhere near as safe as elevated systems, and because they inevitably are involved in accidents, they're not as reliable either.
Just today in Phoenix, AZ, a “violent crash” sent at least one person to the hospital and delayed train service. According to the Valley METRO service, this was the 50th such accident involving the system’s trains since it opened for business a year ago. (Another report calls it a "wicked-looking wreck," and this one quotes a firefighter as saying the van's driver is a "lucky lady to be alive" and that delays were expected to last several hours.)
That record – which includes injuries, property damage and delayed service – is something Honolulu will avoid when its elevated project is completed in the next decade.
Safety is one of the major issues that distinguishes grade-separated transit systems from at-grade systems, but there are others, including carrying capacity, frequency of service, speed, and of course, reliability.
We may not be able to tune down the at-grade advocacy noise. What we can do is note that some of that noise is the crunch you hear when trains and vehicles crash together. That’s noise we definitely don’t need in Honolulu.