I believe the Sandy Hook shooting happened. I believe this because of what I regard as the weight of probabilities. A friend of mine, however, thinks the whole thing was orchestrated by Obama in order to take our guns, and he's very skeptical of the news reports and beliefs about people's motivations and so on that I've relied on to found my view. Now, both of our viewpoints fit all the facts as we see them. So, is there anything at all that makes my viewpoint more reasonable than my friend's?

Good question! Conspiracy theories are, indeed, very interesting cases for epistemologists (philosophers who think about evidence, knowledge, and beliefs). I would say that, on the face of it, and at least in this case: yes, there is something that makes your viewpoint more reasonable. Let's call your theory "A" and your friend's theory "B." What are the implications of A? Just that someone who is mentally unstable and owned a gun committed an atrocity, and the news reported it on the basis of interviews, police statements, hospital interviews, and video footage. What are the implications of B? Obama "orchestrated" the whole thing. Obama and his agents paid off (presumably) hordes of people at the schools, out on fake funerals, tricked or enlisted local police representatives to lie about being there and catching the culprit, deceived or enlisted dozens of professional reporters, and so on, all in the service of...swaying public opinion about gun ownership, even though it is to be expected that an event like this will actually change very few minds and galvanizing opposition to gun ownership will have a very low chance of actually changing the law. Whew. Ok, now we have some shared background knowledge that bears on which of these sets of implications is less likely. It is extremely unlikely, given our background knowledge of the way people operate, that these dozens or hundreds of people involved in B would execute the plan perfectly, without a single slip up or leak, and furthermore that Obama and his crew would risk criminal charges (let alone impeachment) in order to set up a relatively ineffective mechanism for *sort or* galvanizing *some* support for gun restriction laws. On the other hand, given our background knowledge of the way people operate, how likely is it that, of the millions of people in the US, one of them owned guns and lost his mind for a while, and committed an atrocity? Not so unlikely; this happens, and can be expected to happen. So, unless your friend also has an alternative theory that explains why we all believe the things we do about human capabilities and human psychology (and presumably that can't be Obama's fault...I got my background knowledge of people from just living among people and being a person), I'd say your theory, A, is way, way more likely than your friend's theory, B.
Interesting further question: why would your friend believe B, given how unlikely it is? I think we account for this. You friend has a bunch of interests and desires that make concluding B much more attractive than concluding A. These interests and desires may include: paranoia about people taking his guns away, belief that Obama is awful and is a symptom of all that's wrong with our society, desire to feel superior to the "masses" who trust the news, and so on. This could, predictably, cause your friend to subject evidence for A with withering scrutiny (since he wants to avoid A), while accepting any hint that B is true as decisive evidence (since he wants to conclude B). This is classic wishful thinking, or "motivated reasoning," well documented in many, many studies.
That's my two cents.....then again, maybe I'm part of the liberal academic elite trying to twist your mind by introducing this analysis so that you vote the way my masters want you to vote....how can you decide? I say: use your reason, be on guard against concluding things just because you'd rather them be true (and also just because you'd rather them be false!). Who has the better argument to fit with your overall experiences?

Read another response by Yuval Avnur
Read another response about Rationality