Conversely, if you as the sender get a bounce at least you know something went wrong and can try a different way to contact the other person (different email, telephone, text message...) Bouncing is the traditional approach, and the original ethos was "bounce, or defer, or deliver, but don't ever accidentally or deliberately just drop an email on the floor".

It depends whether you think of "the user" as the sender or the re cover -- as a (human) sender I'd rather get a bounce than be silently ignored in a spam folder, but as a receiver I prefer the grey-area emails to be accept-but-spamfolder, not bounced...

As a user, I'm thankful I don't need to sift through hundreds of spam emails a day to find potential false positives. Because that's what you're advocating. You'd apparently like everyone to have a terrible email experience for the sake of your own personal comfort and preference (self hosting your emails).

Besides, for something truly important, the people or organisations who need to reach me know how to do so other than via email (phone, chat, postal mail...).