Agree with this... QT is always good... I don't QT either. I have however found a 'method' that works for me and my tank, my fish are immune to both ich and velvet (except my Mata tang, the latest addition who is suffering from velvet atm. He'll pull though and be immune like the rest) and possibly brook too.Already mentioned that.
Also mentioned IF given the chance. They WILL attack a host. So do your best to keep them healthy. That is all you can do when ich is present in a tank.
There are plenty of fish and shrimp that take care of other marine life of these parasites. They are smart enough to let them do their business on them. You don't need to dive 300 or 10,000 times to figure out there is a balance in the ocean.
You also have to figure 80% of people do not have the money or care to do QT. I do not qt. Should I yes. Should everyone yes. Even when a person qt's down to almost the last drop of water. Something slips through the cracks.
When talking about ich with opinions or methods. They do not matter if you are looking for a cure all. There is only one and it is highly not a good one for the stress/poisoning of a fish, but it is all we have for the cure all.
All my experimentation and reading came after my tank contracted ich... one of the problems is that we only find out a lot of the info out there after the event.
I'm a mod on a UK forum and look after the disease section... despite my own methods I would always recommend to remove fish, treat with copper or CP for 30 days or TTM followed by leaving the DT fallow for 76 days... but that's because the question is always 'how do I get rid / eradicate / cure ich'... I get quite excited when someone says 'how do I live with / manage ich' as that is absolutely possible too.