If this was an "occasional" problem, there wouldn't have been a dozen blog posts on HN about it in the last week (least of all this one). If humans are doing anything sub-optimally that's something technology can help improve. The more common the problem, the more likely there is a common solution.
If everyone wants to use email as a todo list, you have two options: 1. tell everyone not to 2. build it
Option 1 will not work.
In other words, there are a myriad of poor choices being made by people that either cause security issues, or inefficiencies using email as a medium that is suboptimal.
Users are not "broken".
Email is simply a method for people to communicate. People are messy. Put two of them together (communication) and the messiness increases exponentially.
Have you ever seen two people arguing, and then it turns out (much later) they were arguing about two completely different things, and they are actually agreeing with each other? This isn't a technology problem, speech isn't "broken".
Have you ever sent a text message, and the other person didn't respond for a few hours and you started to think that they were upset, or something you said was wrong etc. Then it turns out their phone was turned off or they were in a movie theatre. Everything was fine! Does this mean people are "broken"?
The argument going on in this thread is far too black and white to apply to reality. People live in the grey area. Part of being human is managing the messiness of interacting with other people.