This was one of my defense mechanisms! I still volunteer but now since I'm aware that I was using it when I was upset about something I no longer use it for that purpose, you know, making the unconscious conscious. So no, not all altruism is a defense mechanism but some of it might be.

Really, me just being aware of this released so much of my defensiveness it was almost unbelievable. (I released so much of it that I didn't need my defense mechanisms anymore to deal with it!)