An adoption blogger I follow posted that simple question on Christmas Eve morning and asked adoptees to respond. I was too busy to think about the question at the time. My (adoptive) brother and his family were coming to open presents and eat dinner later in the day, and the task of preparing dinner had fallen to Jeff and me because my (adoptive) mom has acute bronchitis. But yesterday, in the still and quiet of Christmas Day, I thought about it, and I share those thoughts now.
I (thankfully) have been in the business of adding parents to my life rather than losing them. Same with siblings, aunts, uncles, and cousins. I have lost (again) all of my grandparents to death, so I do know a little about how that loss feels at holidays. I remember the first holiday after my (adoptive) maternal grandmother died, and it was strange. I could feel her presence because I could still envision her in the places I had always seen her, but the fact remained that it was only my memories compelling that presence. It was oddly comforting in the midst of a harsh reality – I could conjure her presence at will even though she was gone.
I think the reason I have struggled at various holidays throughout my life is because I had no image to conjure of my (natural) mom and dad or the rest of my (natural) family. On days when “family” is a central theme, it’s difficult to not have ALL of your family there, and especially when you can’t even envision them. While I was separated from my natural families on Christmas Day, I now have pictures of them in my mind and could easily envision them enjoying the day. And those pictures, from memories of times we have shared, helped to make my Christmas complete.
Becky
Through the Eyes of an Adopted Kid 
I think I’d agree with your theory — on days that are all about family, when you’re being told that all the family you need is there, you feel guilty for wondering where the rest of your family is. Because you’re “not supposed to.” Huh. I hadn’t thought of it quite like that.