People Are Too Often Map Illiterate
I want to pick up on what umaysay had to say about the visual appeal of maps in general, and GIS in particular. I think GIS's most potent weapon is its ability to convey a lot of complex data in an arresting, visually captivating fashion. Humans are, by nature, a very visually oriented species. Think about how we judge the world around us based on visual cues. Look at how quickly and tenaciously visually oriented media has captured viewers. We watch more TV, play more video games and are drawn to the Internet, not just because there is a wealth of information, but because it is presented in a graphical fashion that appeals to us. We judge the world around us on what we see, sometimes for good, if we find an artist we like, sometimes badly, if we let what people look like, or the color of their skin, be the sole factors we base our decisions on. So GIS is very powerful in that it appeals to our visual sense.
The other problem is that there is a perception that maps are "authoritative." I think this comes out of a few different areas. One, maps were not easy to produce. They were labor-intensive and expensive, so maps tended to be products of the elite - or the government. While there are plenty of people who have a natural distrust of those entities, by and large, they are considered reliable sources of information. Although maps have gotten easier to produce and more ‘average’ people can make them, I think there is a mentality holdover from this earlier age, where maps are taken at face value and assumed to be factual representations of the world according to the entity that produced them.
This brings me to my third point, which is that people are mapping illiterate. Students who come to college have critical reading/thinking skills drummed into them (or they should have had). We are taught (in theory) from an early age to read and think about text in a critical fashion. (Who wrote it? What is their angle? Who is the publisher? Are they known for quality?) Even if we don't always apply our critical thinking skills, at least the concept is there. The expression, you can't believe everything you read, is at least part of our semi-conscious life. But how to critically think about maps is something I've never encountered, and I daresay unless you have some specific classes in geography or mapping, you may never have that experience, let alone have had training in how to read them. So you have a populace on a whole that is inclined to like visually oriented material (and GIS definitely has a "wow" visual factor). They think that maps are authoritative and objective automatically, never mind that Joe Schmo just threw together a map using GIS. Plus you have people who don’t really understand mapping and all the complicated factors that play into it (what scale and projection mean) let alone understand how to critically evaluate them. With this you have a recipe for disaster.
GIS can be a wonderful asset to show things that could never be visualized before, and it can be a powerful tool to convey your argument or story, but those same strengths can be troubling, when the ignorance and tendencies of the audience can be knowingly, or unintentionally, exploited.