I have a 125 gallon quarantine system, don't get me wrong, it has it's applications. There's a huge difference between cautiously adding new fish and being reckless with you aquarium, because as you said there are much worse things than ich, and I've had the displeasure of dealing with many if them both professionally in the past and privately in with my own fish.
I also share the desire for a new, current, aquarium based study on ich to address some of the "mysteries" about ich many experienced aquarist have dealt with that go against the general consensus about ich.
I still fall back on the problem that it's nearly impossible to completely prevent all instances of introduction. If you have a large enough tank, with enough fish, enough clean up crew and enough coral additions, eventually something as tiny and prevalent as a protozoan will find it's way in.
What about built immunity? Many people, myself included, have experienced fish building immunity to ich after repeated exposure. I experienced this with a powder blue tang, but I've read about this with clownfish, I believe the study was on tomato clowns, that documented this as well. So, is it better to have fish totally unprepared for a possible infection with ich? Just like we are exposed to the flu daily, yet tribes of uncontacted people's in remote location die in mass from the same disease.
As I reach the point I'm at in this hobby, doing it professionally and privately for many years, and now personally keeping the harder to keep and more expensive fish, I find my perspective on quarantine is changing.
I do think it has a place some times, but many times a fish that would have done just fine in a display died in a futile attempt to prevent the inevitable.
