In response to the discussion question about whether or not discussions of earthquakes, volcanoes and aliens belong in a social studies classroom, I absolutely think they deserve to be touched on. Science classes usually only teach you the how and the why of these things (well, not aliens I guess); they don't begin to touch upon the social impact and psychological consequences. As time moves forward, it becomes increasingly likely that we or our students or all of us will experience some sort of earth-altering event at some point. Whether that happens because of a rogue nation deploying nukes or because of an asteroid crashing into the earth, the social impact would likely be similar- I would probably expect there to be at least some period of worldwide panic and pandemonium following such an event. Students should be mentally prepared for this type of scenario to whatever extent possible; it is ridiculous to think that these things could never happen, and living with the awareness that they can happen is part of being an adult who lives in the real world and paradoxically can help you to appreciate the relative normalcy of your current life. I think the best way to approach these types of possibilities in a classroom setting would be to discuss them from a social impact standpoint: if X happened, how do you expect humanity to be behave in response? Would it be better or worse in developed nations as opposed to third world nations?
In response to the final discussion question ("is there a moral difference between employing nuclear bombs, fire bombing cities, the use of unmanned drone strikes as opposed to using chemical or biological weapons? Should these be banned by all countries?"), I believe there is a moral difference, although I believe that it has more to do with the degree of severity than the essential nature of the crime. First off, drone strikes are on whole different level because of the relative size of the destruction they cause; at least these types of strikes can be targeted in a such a way that civilian deaths are hopefully minimized. With a nuke or a large-scale chemical/biological weapon, you are automatically planning to kill thousands of civilians and, in effect, committing genocide against the people living in the area where the weapon is used. The nuclear weapon is already on the table at this point- we have observed the long-term consequences in Hiroshima and Nagasaki and we know what radiation does to people long-term. At this point, no country with nukes is going to leave itself exposed by getting rid of them completely. The only moral difference with chemical and biological weapons, especially with the latter, is that the effects of these have never been observed on a large-scale before and the potential for creating an even bigger problem than the user even intended is far too great. Let's say the U.S. government decides that we have no choice but to take out North Korea, and decide to go with a biological weapon that unleashes a very infectious disease on the North Korean people. Not only would we have already have committed a deplorable act of genocide, but consider this- what's to stop that disease from continuing to spread into neighboring countries until it eventually makes its way back to the U.S. in the form of a worldwide pandemic? At least a nuclear bomb is limited in terms of the total area that it can effect; biological and chemical weapons that make their way into the water supply could devastate even more massive populations. For all of these reasons, I don't believe there is any justifiable reason to use biological and chemical weapons and I believe they should be universally banned. We've already got nukes on the table- what more do you need?