Pretty well nails it, including the Jon Stewart reference.

1. People are smug about political/religious/philosophical opinions because they think that any conclusion that is "reasonable" holds the same weight as a math equation. But there are different degrees of how sure we can be about what our reason tells us. There are some questions that reason alone cannot answer, and most of these fall in the moral/ethical/political/religious/philosophical areas.

2. People don't understand statistics. We have so many studies and so much data today that you can spin any point you want and make it look unassailable. Drug companies do this all the time. It happens in medicine. The New England Journal of Medicine recently did an article on how consuming chocolate gives you a better shot at winning the Nobel Prize. They used the same sort of methodology that a lot of medical journals use. Not that these methodologies are wrong, but the weight the public often give their conclusions is very wrong.

3. A lot of people are prone to the Dunning-Kruger effect. Essentially, if you see someone bragging about how much they know about a given subject, not recognizing their own ignorance, not appreciating the knowledge of others...that person is probably incompetent in whatever area they are blathering about. People who really know their subjects equivocate a lot when talking about them. It's a cognitive bias. Incompetent people believe themselves to be better at X than they really are. And experts believe themselves to be worse at X than they really are. 

4. People want to sound "scienc-y" but they don't understand science or how it works.

There's probably more. These are just some of my own obervations.