I'm just noticing that I haven't anwered Edgar's original question: "Is Evolution a Dangerous Idea? If so, why?" My answer is yes. Yes, evolution is a dangerous idea.
To see why, you need to understand that Darwinian evolution is an algorithm. Start with a population of individuals which differ somewhat from each other. Let them compete for resources. Let them be fruitful and multiply, copying their traits into the next generation, in proportion to how well they competed. That's natural selection. Moreover, introduce a low rate of mistakes into the copying, giving the next round of natural selection new traits to select between.
One more important feature of evolution is that it can, in principle, run on any
kind of hardware. Given the conditions I just described, evolution just happens. Individuals in the population will continuously improve at surviving; some of them will grow astoundingly complex in the process. All this diversity and complexity can happen without any intention, any mind, any creator in charge. And it can happen to anything. Nothing about the algorithm requires that the individuals, the copying, the mutations, or the selection be biological.
Having understood this algorithm, and having verified that it has brought about the species we know today, people will obviously ask the next question: What else has been passed into our generation by mindless copying? What variations can we try on it? What part of our inheritance can we dump because it no longer works for us? Does it extend to political systems? Social institutions? Laws? Moral rules? Churches?
All these are dangerous questions for authoritarian minds who want there to be a mastermind in charge, and who want to protect our heritage against tinkering and selection. I think they're quite right to think evolution is corrosive of what they hold dear. And it's a good thing, too.