Has anyone ever unfriended you without explanation? Did you ask why? Have you ever deleted someone from your friend list without saying why?
I only unfriend someone if they offend/devalue my core beliefs (i.e., if they're intolerant and view their own values as "right" rather than simply different from my own). And I always tell them. As for being unfriended without explanation, it happens. Sometimes it hurts, but creatures who live inside our computers play by different rules. That makes for livelier buzz with occasional stings.