I've said a lot about being skeptical – but what does that really mean? What I'm talking about here is the concept philosophers might call “scientific skepticism”, which involves questioning assertions that lack empirical evidence. I believe this to be a fundamental part of scientific inquiry. It can be summed up through the phrase “extraordinary claims require extraordinary evidence” (popularised by Carl Sagan) – and obviously that applies well to cosmology, through its grandiose themes, just as it does to pseudo-science. Science isn't completely mechanical and dispassionate, since it includes speculation and creativity as part of the process of development – but that's not the same as accepting every new idea that comes along. At the other end of the spectrum, it's also important not to fall into the trap of “denialism”, i.e. adopting a position that rejects every claim even if there's good evidence to support it (like climate change, or dark matter perhaps).
To be a bit more explicit about skepticism, let me pick the writings of a particular modern philosopher, namely Mario Bunge, who has written extensively on the topic of scientific epistemology. Among other definitions, he describes how any authentic science must include “changeability, compatibility with the bulk of the antecedent knowledge, partial intersection with at least one other science, and control by the scientific community” [30]. These ideas give a little more content to the notions of hypothesis testing, falsifiability, parsimony, etc., that we learn about in school. And they make clear that the skeptical approach is central to the establishment and evolution of scientific ideas.
As examples of topics that fail to meet these criteria and land up in the pseudo-science category, Bunge lists “astrology, alchemy, parapsychology, characterology, graphology, creation ‘science', ‘intelligent design', Christian ‘Science', dowsing, homeopathy, and memetics”. However, Bunge also states that “cosmology is still rife with speculations that contradict solid principles of physics”! He says that for good reason – the SMC lives within the domain of “physical cosmology” and has passed a wide array of tests, but, on the other hand, the most theoretical aspects of cosmology are indeed in an entirely different conjectural realm. Hence it is important to separate the concrete parts of modern cosmology (the answers to the “what” questions) from the areas where we are still speculating wildly (and trying to find answers to the “why” questions).