From Facebook's standpoint I would imagine that these are viewed as completely independent policies. On one hand Facebook does not want to censor discussion, on the other Facebook does not want to host explicit images. The distinction that you draw above simply has to do with their definition of what is an explicit image.

Would you make the same argument if we were talking about Holocaust deniers and personal pornography? Because I am pretty sure that is the distinction that Facebook is making. You just disagree on what constitutes pornography. (I am not agreeing or disagreeing with either of you around that definition either way, just saying that I think you are arguing a different argument).