Conversely, why is scrolling considered evil? We can agree that emails are documents. In real life, on your desk, do spread out all your documents so you could see them all at once? Or do you have a stack of them and view them one by one? You can still cross reference by putting documents side by side, just like you can with multiple emails open in separate windows or monitors.
Admittedly depending on the amount of emails and the speed at which you work through them you might benefit from seeing many at once, though there's other ways of dealing with that issue.
> All whitespace achieves is aesthetics, which are meaningless beyond initial adoption.
I don't think whitespace is all about aesthetics. Personally, it makes it easier for me to read and focus on things. It gives individual things more value, rather than them being "just another thing in a gigantic list", easily blending in and showing no significance.