I generally recommend people have at least a few degrees of kH to help stabilize/buffer a tank and also some slight side benefits of helping discourage calcium leaching from inverts, fish bones, etc.
My KH is 20 ppm, roughly 1 degree, I've found zero support for this over the years, I try and kill snails all day long, I can never rid the tank of them.
It's rare unless someone uses pure RO to a KH less than 15-20 ppm.
CO2 is also acidic and will slowly break down kH.
This is wrong.
A tiny amount of the CO2 gas added converts 1/400th of the KH, but for all practical purposes, this assumed to have zero impact upon the KH by adding CO2. Anyone can add CO2 and then carefully measure their KH .....and verify this repeatedly on any planted tank using CO2 gas. Your KH will not change(at least due to adding CO2).
The addition just changes what is there and then after degassing, the 1/400th of that KH is restored. It is not destroyed. Even if you lack all the alkalinity, 100% gone..........adding the same flow rate of CO2 gas will still yield pretty much the same thing, 399 vs 400 is a mere 0.25% difference, something we could not detect in a planted tank.You could not use the pH/Kh to measure CO2 this way (there's no HCO3), but, you could add a little bit of KH, then remove it, and keep the SAME CO2 gas flow rate and be able to assume safely that the ppm's of CO2 would be within 0.25% of the KH vs the no KH test samples.
This KH, CO2 and acid base stuff gets most hobbyist.
Someone doing regular water changes with average parameter tap water should not notice dramatic fluctuations in their kH levels.
If someone's tank or tap water is bottomed out on kH, it's easy and cheap to raise, lots of common products on the market. Baking soda is easy if all you need to address is kH.
I tend to recommend using something like Seachem Stability to reconstitute other trace minerals as well, for anyone using RO water for water changes.
Again, unless someone has extreme tap water parameters or has a goal of keeping/breeding some very specialized fish species, most hobbyists don't have to worry too much about their kH and gH and can work with what comes out of their tap and just do regular water changes to keep the tank parameters stable.
This is factual.