The harm is not just half a second to delete an unwanted email.

There is also the cost of: seeing that I have an unread email, switching to my email app, and working out that it’s spam.

If this gets normalised, it will not be just one spam email. There will also be the time to classify and delete spam emails from everyone else who feels entitled to spam me.

There is also the cost of incorrectly deleting a non-spam email, because you’re on a hair trigger because of all the spam you get.