I have heard this asked quite a lot of atheists. Why are atheists so active in religious discussions if they do not believe in the tenants of the religion? Neil DeGrasse Tyson is often labeled an atheist but adamantly rejects that label because he feels much the same way. He once compared it to golfing, stating that he does not golf at all, so why would he want to spend any time discussing it? Well, if golfers were constantly directing their golf balls into your car windshield, you then might have something to say on the matter. The same is true for religious discussions - religion is a MAJOR part of our society and effects EVERYONE, not just those who believe. Many of those effects have been severely detrimental. In the case of this particular thread, the pope's comments are down-right insulting to non-believers. I can (and am) a good person without belief in god. My sense of right and wrong is not dependent upon any ideas of a supreme being or higher power instilling those attributes upon me - the same can be said for most believers as well, they just don't admit to it. For the pope to imply that, even though I am not a believer, because I am a good person I am following his god is an offensive attempt to inject his god and credit him for the morality and decency that I have. It was not his god that grew up in a universe that must be shared with other human beings, it was ME! I wish to live the best life possible for as long as possible because I understand that I will not be getting a second life when I die, so, in order for me to live the best life possible, I must understand that I share this reality with others, and I must recognize that my actions have consequences, and, as such, I will avoid, whenever possible, those actions which have negative consequences on myself and others. I have come to an understanding about the nature of the reality that I live in, I have achieved this understanding - it was not instilled upon me by some higher power. Religion and religious tenants are not paths to morality. There is no system in religion for determining what is moral and what isn't. Religion does not allow us to understand morality, religion simply makes moral pronouncements. There is no method, or reason behind it.
Having no beliefs does not mean you don't care about religious beliefs, or do not want to actively participate in discussions about religion. In fact, as you can clearly see, the exact opposite tends to be true.