Skepticism is nothing new. In ancient Greece, Pyrrho of Elis (360-270 BC) questioned everything and withheld assenting to all beliefs. The Roman Sextus Empericus (160-210 AD), who idolized Pyrrho, took skepticism one step further and developed a very sophisticated methodology for questioning the foundations of all types of knowledge. This school of skepticism, known as Pyhrronism, sought to free minds from the disturbance of unfounded beliefs. Much later, one of the greatest modern philosophers, David Hume (1711-1776 AD), drank from the same fountain as these ancients. Although he had positive philosophical beliefs and contributed to fields like economics, history, and proto-psychology, Hume laid siege to many sacred cows like causation, foundationalism, the design argument, traditional ethics, and miracles.
These Pyrrhonian skeptics, despite their brilliance, did not get too far when it came to attaining positive knowledge about the world around us. This is because their skepticism was predominantly focused on tearing down or undermining knowledge. Not constructing it. Scientific skepticism differs from this philosophical skepticism because it is not satisfied with merely questioning beliefs. It also wants to find out the how the world actually works and which methods are best for exploring it. To succeed at this task, the skeptics of our age have embraced, as Michael Shermer put it, "the most powerful tool ever devised for understanding how the world works." This tool is science.
What impresses skeptics about science is its long track record of successful prediction and potent application in fields like computing, medicine, and engineering. In the short time since the Scientific Revolution, science has explained the origin of species and shown us that our Milky Way galaxy is one among billions and billions. Most notably, it has eradicated diseases like Polio, made instantaneous communication around the world possible, and put men on the moon. The skeptic is equally as impressed by science's methodology. Unlike traditional ways of looking at the world, science is built on probability rather than certainty. This means that all knowledge in science is fallible and can be revised if new information becomes available. This track record and its openness to new ideas is why skeptics are confident that science is the way to go.
Science has many valuable lessons to teach us. It stresses the importance of admitting when we do not know something, it uses Ockham's Razor to shave off auxiliary assumptions, it requires that we know how to tell the difference between legitimate and illegitimate resources, and makes us demand extraordinary evidence for extraordinary claims. When we put these virtues, along with knowledge of cognitive biases, logical fallacies, and the history and philosophy of science, into a toolkit, we get a non-domain specific form of reasoning called "scientific skepticism." This toolkit helps us inspect a vast array of weird things like the laws of thermodynamics, haunted houses, homeopathy, and the idea that humans are distantly related to corn. It places them on a truth continuum which ranges from almost certainly false to almost certainly true.
It is true that all of this knowledge is not certain and may be revised, but it would be mistaken to think that this allows us to not take any of these ideas seriously or that we can believe whatever we want. There is so much evidence and corroboration for the ideas on the "almost certainly true" part of the spectrum (evolution and thermodynamics) that it would be perverse not to accept them. Likewise, the evidence points very strongly against ideas on the "almost certainly false" part of the spectrum (haunted houses and homeopathy). Our tendency to place all sacred cows on this continuum according to their supporting evidence has led to my fellow skeptics and I to be called "rude," "cynical," or even"close-minded."
While it may not be polite, we skeptics value the truth above all else. As Carl Sagan once said, "it is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring." If we do not, as Carl Sagan asks us, seek the truth, then we are susceptible to being taken advantage of by others. Every year, thousands of dollars are thrown away calling psychics and reading horoscopes. Think of all of the people this money could have fed or how many people it could have put through college. In some cases, people die from using faith-healing (no, I am not kidding). If only these people would have been more skeptical, their lives could have been saved.
If this view of the world sounds interesting to you, then I highly recommend reading Carl Sagan's essay The Burden of Skepticism. This essay beautifully written and is full of lots of great information. You can also check out Brian Dunning's Here Be Dragons. This 40'ish minute video fleshes out a lot of the points made in this article (it is also classroom friendly).