Again, it is only what works for me and several other seasoned veterans. There are plenty of others with much experience who, like you, QT vigorously. Eventually though, you will see that it happens. And when the parasite DOES make it in to your system, it will wipe out everything. This will leave those of you in this camp even more firmly planted in your belief that these parasites are nearly always fatal. In reality though, they had no defense as a result of what was well-intentioned fish husbandry, IMO.
Ha ha, OK, looks like we've got 'seasoned veterans' on both sides of the aisle. I'd suggest you are making a couple of erroneous assumptions about what I may or may not think (you know what they say about assumptions). Ironically, I'm actually somewhere in the middle on this debate as I do have a mild ich strain in my tank; I QT because at the end of the day ich can be managed and is certainly not always fatal, but I really don't want velvet, brook or uronema (just to name a few) which may not be manageable. All I can tell you is that in the last 10 years of keeping reef tanks my fish losses are far lower than in the first 15 years. OK, I'm a better reefkeeper now than I was, but I think an effective (though not perfect, I grant you) quarantine has been central to that success (I don't lose fish to the QT process in the main). Lastly, I find the 'exposure' argument to be a rather weak one. If I keep a healthy, previously quarantined community of fish, and a parasite is inadvertently introduced, then there's an opportunity for them to be 'exposed' and begin to develop said immunity (if indeed that's really the case). How is that any different than plopping a fish into an already infected environment?
But, at the end of the day, we each do what we think is best and multiple approaches can be made to work, with inherent pros and cons.