FWIW, it is possible that, in these wild days, we are naturally inclined to read something into this section that is not actually there. I may come to see what others now see, but, at the moment, I just see him saying, roughly:
"There is a common enemy that is about finish the job of enslaving all of us. We need to set aside various differences for the time being or we will all be toast. Yes, we have our differences, but acrimonious discussion of them does not help anyone at this late stage of the game -- as it unnecessarily exacerbates a division that the common enemy is using to conquer us all."
I am NOT saying this perspective is or is not the BEST approach -- but that this is how I read the portion in question. IOW, I see the advocating of mutual assistance on a temporal level in order to effectively resist a common enemy, but I do not see that the author is advocating any kind of religious union or cooperation. MP seems to be saying, "However substantially we disagree about certain things, we will all soon be toast if we do not work together in order to expel/eliminate the common threat."
I am quite open to being shown that my understanding of MP's meaning is wrong. Further, I totally understand that there really is no solution outside of that which the Church has always taught. Our MAIN problem IS, in fact, spiritual and, therefore, all other measures will, in the end, amount to nothing, should we fail to be converted in heart. In that sense, this passage might be tainted with a naturalistic perspective, but that is not the same as actually and openly advocating inter-religious dialog. One might argue that such a perspective is a step in that direction, but that does not equate to having already arrived at said destination.