What's wrong with vanishing scrollbar? I prefer them this way. The first thing my emacs config file does is to hide scrollbar.
Design is always a trade off. Do you want more focus on content, or more information with less focus? Is your default setting more friendly to smaller or larger screens? Every person has different preferences, and every trade off has cost benefits you can run. Yet your statement here is very “black and white” (ahem), assuming everyone should think like you. That betrays a lack of nuance in understanding how design works.
In the programming world, you also have these trade offs, yet it’s easier to avoid thinking about them at times. Static vs dynamic languages are full of trade offs like this.
To avoid coming across as yelling at clouds, attempt to frame why it’s a trade off you prefer, rather than a platonic ideal others don’t see (because it isn’t).
It would not be the right choice for a default config, or in a context where sometimes things are scrollable and sometimes they aren’t. (This is often the case on mobile phones; if there’s no scroll bar, the only way to tell if something is scrollable is to try it, if you think to.)