I am not sure how to follow any of that logic. The municipal supplies are chlorinated due to codes, laws, and liability. If a city supply were to be contaminated with a dangerous pathogen, it could affect hundreds of thousands of people, not just a single family. Chlorine can be safely removed from the water supply once it reaches your house, just like a private well system.
And back flow/cross connections etc, this is why codes are in place, to prevent this potential cross contamination, especially from potable to sewage. Proper air gaps, back flow prevention etc is critical on shared supplies.
Just like any water treatment system, proper maintenance is important. GAC can grow bacteria, but bacteria in and of itself is not bad. It is the type and quantity that matter. All water supplies have organic matter that occurs not only from living organisms and from decaying matter in source water, but also from the water treatment processes and distribution system materials. The relationship between microbial growth, biofilm growth, etc. within plumbing and distribution systems can be shown by TOC levels. Water treated by multiple sanitization methods will begin to show raised TOC levels as soon as the sanitization method is removed. Chlorine, Ozone, UV, sub micron filtration etc can all be used to reduce TOC, but once these methods are removed (when the water leaves the UV chamber) TOC levels will immediately start to rise, again indicating organic growth.
A GAC filter is highly recommended for removing chlorine from a potable water supply prior to drinking, bathing in, or breathing the vapors. That being said, proper santitization methods should also be implemented for any plumbing system that is not chlorinated. Material choices, dead leg considerations, source water etc all must be considered when it comes to a proper sanitization protocol. Changing the GAC filter media in a whole house carbon tank is cheap and easy and when it is changed, the tank and other components should be sanitized at that time. Every few years is adequate to minimize biological growth in most residential applications. Same goes for a simple carbon filter under the sink, or an RO system, but annual changeouts is considered adequate. Regular sanitization is important, again to reduce, not eliminate microbial growth.
If you ever get the chance to tear apart a 15 year old refrigerator with a water dispenser, it is a perfect opportunity to see what is going on. Many refrigerators have a reservoir in the refrigerator allowing for cold water dispensing. If the refrigerator has always been fed with a dechlorinated source, IE a private well or a GAC filtered system, you will likely find massive disgusting looking growth inside the cold water storage and even the tubing. is this dangerous? Probably not, but is it desirable? No.
I have cut open piping systems that were barely flowing water anymore due to the pipe being almost entirely filled with a slimy gelatinous biofilm. These were usually on "dead legs", places where water rarely flows, an unused bathroom, etc.
Dechlorinization is an important water treatment process to consider, but make no mistakes, private wells are not magical happy water sources that vary tremendously from municipal sources. Most municipal sources are minimally treated, and many are from the municipalities own private wells.
Hope this is helpful