I assume your definition of pacifism is "the refusal to engage in martial activity because of one's principles or beliefs." If it is "the principle or policy that all differences among nations should be adjusted without recourse to war" then I would say IMHO, that we as Aikidoka should all be pacifists. But as Mochizuki Kancho taught us, specifically in his lecture at the Second Aikido Friendship Demonstration, that to survive we must be strong.
As I said before, it was not O'Sensei's religious beliefs that changed him after the war, it was the war itself! O'Sensei used to teach military academies and was friends with admirals and generals. Men like this then declared decided that Japan should enter the war. As a result the country he was born and raised in was bombed and burnt beyond belief. I think this would change anyone who had a martial way of life, and they would think about what the purpose of that martial way was.
I respect what you are saying. Peace is always the better choice. I love Pre WWII Aikido, what else can I say!