Viewing pane in Email clients

After looking at Joe's Email client editorial, I realised it shows the viewing pane of an email.  I always advice people not to have this visible as there could be a threat of viruses if the email is HTML.  With this in place you don't have an option as to whether you wish to open it or not, especially if its the only email you have downloaded.   Just having a listed view of the emails is fine and therefore not open and you can just delete them before viewing.  Am I right in this thinking?

Tony