[This is also posted at the Canberra Skeptics Blog]
Everyone is sceptical, it's by necessity since there are a whole bunch of different contradictory beliefs out there. And while someone can hold two simultaneous contradictory beliefs, we can recognise that in general being for some particular beliefs means rejecting others.
Consider explicit scepticism such as the anti-vaxxers and 9/11 truthers. They don't accept the mainstream explanation for whatever reason and instead substitute in their own. Then there are those who engage in implicit scepticism, by pure virtue of holding a contradictory position. Think of the creationist who believes in the inerrant word of God, or the psychic who talks to the dead and what that implies.
Yet we don't consider these people as Skeptics. While they are sceptical these are the people we consider credulous. That should tell us something about what a Skeptic is. Then there's the notion of philosophical sceptics, the ones who have walked the path of the Cartesian demon and found themselves but not a way back. And while we are at it, let's not forget the post modernists who have turned knowledge into a cultural construct.
Each of us is sceptical in our own way, but we aren't Skeptics. When Bill Maher rants about Big Pharma, we as Skeptics realise he has reached a failure in critical thinking. Because being a Skeptic is not just doubting stuff, it's taking on the maxim that belief should be proportional to the evidence. Bill Maher shares the distinction with anti-vaxxers and 9/11 truthers and creationists in that the sceptical position is not taking into consideration the relevant evidence.
There are good reasons to be sceptical of Big Pharma, but is that reason to dismiss all products that Big Pharma produces? Surely one should be looking at the success of the product itself, something that is verified through empirical peer review. Just as the failure of 9/11 truthers is by which they create a more implausible narrative, implausible because the evidence is against it. Not just the lack of evidence but of the evidence underlying the explanation.
I'll expand on that point. When someone alleges that crop circles were made by alien craft (sceptical that people could make them) they are alleging something involving the great distances of space. We don't know if it's even possible to participate in interstellar travel, let alone that life capable of doing so exist. The narrative involving aliens has plenty of evidence against in this respect, what we know about the universe makes such an explanation highly unlikely.
Likewise the 9/11 truthers are making an evidential claim about behaviour that just doesn't make sense. The more people, the harder it is to keep a secret. More people to leak it, more people with a conscience. It's inventing more implausible narratives at each step to explain the first implausible narrative. Even without an explanation, a grand conspiracy is a bad one.
It is not enough and cannot be enough just to doubt stuff, because doubt is always filtered through our preconceived notions of how things are - be they intuitive, taught or experienced. It's no surprise that people who are sceptical of evolution so easily see an intelligent agent behind the complexity, or that 9/11 dictates a more ordered explanation than a few fundamentalist Muslims hijacking planes.
Even in the case of medicine where extensive testing and use means that side effects are disclosed, we hear about drug recalls and doubts over their safety all the time. Yet we seldom hear about "alternative medicine", the dangers of chemotherapy sound horrible but a homoeopathic cancer remedy is side-effect free.
To echo Carl Sagan: "extraordinary claims require extraordinary evidence" because a claim is extraordinary because of how much it diverges from the way we know the world works. It's easy to be sceptical of claims, but to be a Skeptic is dedicating oneself to the notion that belief should be proportional to the evidence. Doubt is a good starting point, but only if it applied to all ideas. To dismiss vaccines while taking homoeopathic vaccines is not being a Skeptic, just selectively applying scepticism. A Skeptic should be open to the possibility that they are wrong however difficult that is to do. Why? Because if we can't do it then how can we expect others to?