That's a great concept if everyone knows ahead of time what the "proper maintenance" is to begin with. Unfortunately, there are a lot of pet stores out there who are uneducated and worried only about making money. I have seen too many tanks where they have misadvised as proper, only to over stock with incompatible fish, yet, too. I deal with that on a regular basis. Once a person understands the hobby, they can make the decision to use it or not based on education rather than guessing. Any beginner should use carbon until they understand water quality and how to keep it safely balanced. The advice of never using carbon leaves those out there with 10 Goldfish
tanks, "because the store told them it was ok" at risk of major crashes that can be made to work temporarily until they can fix it, but carbon will be one of the keys to buying a few days or weeks of time. There are many horror stories out there, and unfortunately, until the stores are educated and teaching it, people will still go home with a fancy Goldfish
or 2 in a bowl to watch them swim... until they go belly up, "because that's what fish do, right?"
I have worked with this so much, and it's so sad. My work and training have taught me to error on the side of caution when a life is concerned. It takes time for people to learn. You've had 10 - 15 yrs of experience to learn, where others have not. I still prefer the advice I gave to begin with, it's safer and covers more of the population than not. In a perfect world, everything would be healthy and happy, and we'd automatically know how to achieve that. This world is not perfect, and there are also others out there who know the risk, yet take the chances "just to see what happens". They are part of the "hold up" with our imperfect world improving. I have been exposed to the "general public" of customers, and I have to be honest, 70-80% of them are simply "irresponsible and uneducated customers", and about 50% of those are inhumane in their practices for entertainment purposes.
I recently talked to a man who owns a 30 gallon cube saltwater tank, and in a matter of 8 months has managed to kill many fish needlessly, and continues to believe that he knows best. In this tank he had a clown trigger, a dogface puffer, a large angelfish, 5 domino damsels, a coral banded shrimp, a tomato clown fish, a bubble anemone, and snails, hermits, and a 6 inch tang. These fish were all added to the tank within a 2 wk period, and as they died they were replaced with another of the same kind... over the course of 6 months. The pet store never advises him against his purchases so long as he spends the money, nor have they told him what any of these animals needs for care. He feeds pellet food only, and couldn't figure out why some of his fish didn't eat or appeared to starve to death. This is more common than many people may realize, and the advice I give is meant to error on the side of safety first, to give a person the chance to learn what is needed before trying what I consider to be "advanced techniques" in todays day of fish keeping.
I am happy that your tanks have been successful, that is encouraging, and many more will get to that phase of learning and accomplishment... over the same course of the 10 - 15 yrs you have now. Because of technology and business, fish keeping is not what it used to be, which is a sad thing. Too often I've been asked to provide a customer with a "no maintenance aquarium" and then insulted and yelled at when I explain that there is no such thing that exists when you are talking about living animals. I finally began sending people to the toy stores for the plastic fish that float in an aerated tube of water, with decorative light to show it off. If they were extremely rude, I would point out that even something like that requires dusting if you wish to see it long term.
If the world were a better place, if society had different views and practices, your advice of no carbon regularly would be a normal practice and would work. Right now, there simply isn't enough education happening in the places it needs to.
This practice can be learned... but without the learning, it can cause a lot of problems, making a lot of animals suffer while someone is learning. I am here to help prevent that while the education is being presented at the same time, so everyone can achieve the most natural and healthiest process of fish keeping as is possible.
BTW, leaving the carbon in long term as you described is also dangerous. It works like a sponge, and like a sponge, when full, will flush the pollution back into the tank. In a situation like that, it would be safer without any carbon at all. Carbon should be changed after 30 days if it is being used.