I know it does warn that it will block the user upon deletion. However, I like the contact list clean up where it shows all the details of the user in one window, unlike WLM's contact list where you have to hover over the user to see the email and determine who is who, especially those people you havent talked to for ages and you'll be like hey who's that and all.
Maybe it would be possible if there were 2 buttons in the clean up window like "delete" and "delete and block", I don't like to delete my contacts from the contact list itself because its not as good as using the cleanup window