I understand your points and they are valid. And I agree that using HTML in posts is dangerous, if many people are adding to the site.
But my site doesn't have editors or outside contributors. And I'm guessing there are others like me in that regard.
Posts and pages are major means of showcasing elaborate content. Calls to PHP are another. In any case, since there is an HTML editor, I can state that -- for me -- being able to comment out code temporarily and leaving it for possible future use is a feature I would like.
Still, I can see where you're coming from. My main point is that, whether commenting out code (or even adding HTML elements) is good or bad, it is permitted. So, the ability to occasionally comment it out, as is common practice in other environments, would be useful. I can work around it by saving code and reinserting or, in some cases, by simply switching to "display: none;" from "display: inline;".
So, on reflection, if this doesn't seem like a good feature to WordPress developers or if it is considered outside the community intent, then there are more important things to focus on, and I withdraw my request. Thanks for considering this.