It would appear to me that soy milk should be as permissible as peanut oil. Rav Moshe Feinstein (ig"m o"h 3:63) permitted the consumption of peanuts in a community that did not have a custom to the contrary. I would assume that it was on this basis that the OU used to give a hashgacha to peanut oil. Despite Rav Moshe's lenient approach, it is clear that the "community" chose to be more strict.
Based on Rav Moshe's logic, soy milk should be the same a peanut oil. Peanuts were not part of the original decree of kitniyot. That being the case, we ought be permitted to be lenient regarding the liquid form of peanuts. Soy beans were not part of the original decree. That being the case, we ought to be permitted to be lenient regarding the liquid form of soy beans – soy milk!
Despite the fact that my entire family drinks soy milk on a daily basis and that my kids never drink regular milk at all – I was not willing to be lenient.
The raises the extremely challenging question of who defines the parameters of our "community"? I am not sure what the answer to this question is, but I would be curios what people think about this issue. Are we defined by the teshuvot of Rav Moshe Feinstein or the writings of Rav Soloveitchik? Is there a single person, or group of people that would define the boundaries of our community? Please share your thoughts…