Well, it's a traditional form, that's all, and we all participate in a great many traditional forms that we don't necessarily believe in every single detail of...but as long as we believe in the basic objective of the tradition itself, we do it. I take it you do believe in the basic objective of the presidential oath?

During my 10 years in American public schools, I did not participate (as everyone was required to) in the daily reciting of the Pledge of Allegiance to the Flag. That is, I outwardly appeared to be participating...no point in openly fighting that war with the whole apparatus all around me at the time, it would have been foolish to do so...but I mumbled and didn't actually say the required words. This was because I had no allegiance to the American flag, none whatsoever, and I wasn't about to say I did. I did not believe in the basic objective of the ceremony....since I was not an American citizen, and I was missing my own country and wishing I was back there.

I was also an atheist at the time, but I didn't feel bothered by the mention of "God" in traditional speech forms such as "God knows" or "So help me God". I took them as common customs, not statements of categorical belief in a deity. Anyway, people mostly use the word "God" in such phrases simply to add emphasis to what they are saying.