He prefers it to blackboard. It's a very idiosyncratic preference, IMO. I'm pretty sure I could refuse and he would have to oblige me; however, maintaining a facebook account with 1 friend isn't a big problem.
Yes, I deleted my Facebook account in early 2010. However, I have since created a placeholder account to buy ads and admin a business page for my company. I've logged in exactly once in the past 2 months.
Like you, I had but then deleted my facebook account; however, a professor of my grad school class requires one, so I created a temporary account.