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As for commercial/public use, obviously one does not want to overuse CYA, but the real ignorance is in not understanding how a modest amount of CYA moderates chlorine's strength enough to not be too harsh on bathers and enough to reduce disinfection by-product production but not so much as to prevent adequate disinfection. This is known science since at least 1974 (more on that later).
Note that they refer to a buildup of CYA -- there is no buildup to high levels with the Dichlor-then-bleach method we propose. We only use Dichlor until the CYA reaches around 30 ppm and then switch to using bleach. Note how this is superior to what most residential spa users do which is Dichlor-only with CYA buildup. However, if you were to not have any CYA at all, then the chlorine would be too strong, would outgas too quickly, would degrade hot tub covers faster, would oxidize swimsuits and skin faster, would corrode equipment faster, produce disinfection by-products faster, etc.
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I suggest one reads the "Chlorine/CYA Relationship" section in the first post of the thread
Certified Pool Operator (CPO) training -- What is not taught. It gives numerous references to scientific papers explaining that relationship so that people no longer need be ignorant about the subject.
Again, the above shows ignorance for what CYA actually does and the public health references are for commercial/public pools and spas, though even so they still show ignorance of the actual science of the chlorine/CYA relationship. They all think that CYA's only role is to protect chlorine from sunlight and that CYA's reduction of chlorine effectiveness is so extreme that it shouldn't be used, but yet they do use it outdoors. The fact is that CYA is a hypochlorous acid buffer so one can tune the level of active chlorine one needs for appropriate disinfection and oxidation. CYA acts as a reservoir for chlorine so that you don't run out of chlorine which is something that is the primary reason for problems in the MMWR reports (there are a few reports with excessive CYA well over 100 ppm that are obviously problematic, but most are about near zero chlorine levels). CYA also moderates chlorine's strength. Using chlorine without any CYA can have the chlorine level be too strong. Europe understands this which is why their DIN 19643 standard targets 0.3 to 0.6 ppm FC with no ozone and 0.2 to 0.5 ppm FC with ozone in the circulation path. Higher active chlorine levels lead to faster oxidation of swimsuits, skin and hair and to faster creation of disinfection by-products. This is basic chemistry -- a higher concentration of a reactant results in faster reaction rates in whatever reactions for which the reactant participates.
My wife has personally experienced this difference in chlorine's strength where in an indoor commercial pool she used to swim in every 5-month winter season we would have to replace her swimsuits every year and her skin was flakier and hair frizzier compared to our own outdoor residential pool she swam in for 7 months of the summer season where swimsuits would last for 7 years and the effects on skin and hair were far less noticeable. The chlorine level in the indoor pool was 1-2 ppm FC with no CYA, but in our outdoor pool it was 3-6 ppm FC with 30-40 ppm CYA but that is equivalent to around 0.1 ppm FC with no CYA. It is the factor of 10-20x difference in active chlorine concentrations that accounts for the different experience. Essentially, the indoor pool is significantly over-chlorinated in terms of the active chlorine level. Had the indoor pool used 4 ppm FC with 20 ppm CYA, it would have had an active chlorine level of 0.2 ppm equivalent with no CYA.
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There is a reason I'm only in it ~15 minutes.