I always hate answering this question because, at this point, the majority of people know Wicca clearly isn’t Satanism. They don’t even consider the question. However, it still comes up enough to merit mention here.
There is nothing slightly Satanic about Wicca. Wiccans don’t even believe in Satan or other inherently evil entity. Good and evil are choices that each of us makes through free will, not a force of nature ruled by a god. Each of us has the possibility for both. “Evil” by definition is nasty, cruel and unpleasant, and we certainly would never encourage anyone to behave in such a manner.
Why do people think it is?
This question is quite a bit more complex. For some conservative Christians, all non-Christians (often employing a very narrow definition of Christian) are agents of Satan. Hindus, Buddhists, Muslims, Jews, Atheists, Scientologists, Druids, Wiccans, whatever. There’s nothing we can do about that. It is their right to hold that belief. However, there are people who associate Wicca with Satanism even if they don’t associate other religions with it, and that deserves more coverage.
Part of it is Wicca’s ties with witchcraft. Many Wiccans are also witches, and many people are still using the older definition of witchcraft: follower of Satan or worker of maleficarum i.e. harmful magic. They hear the word witch and they associate bad things with it. They do not understand modern witches are using a modern definition.
Part of it is appearance. Think of the images Hollywood for Satanic rituals: robed figures standing within a circle, pentagrams, ritual daggers, candles, incense, and so on. All but the robes are standard pieces of Wiccan ritual, and some Wiccans use robes as well. A lot of this comes from 19th century magical orders such as the Hermetic Order of the Golden Dawn, from which both Wiccans and popular imagery of Satanism draws
Isn’t Wicca about hedonism?
Not specifically. Wicca has far fewer taboos than traditional Christianity about personal behavior, but so do a lot of religions. Being happy is not a sin. There is nothing wrong in enjoying the fruits of our labors. Things like sex and food are not bad things.
Christianity’s tendency to equate the material world with Satan is a stark contrast to Wicca’s view of the material world as being intrinsically united with spirituality. The material world is a part of our theology; understanding it helps us better understand the divine rather than drawing us farther from it. The gods gave us our senses not as temptation but as tools through which we can better examine the world.
I am not suggesting we act wantonly or carelessly. Actions should always be responsible. Taking advantage of others for your own satisfaction is evil. Excess is undesirable. And while Wicca does not condemn many behaviors rejected by conservative Christianity, neither does it require them. Instead, Wicca encourages us to find healthy, happy and responsible choices.