Religions tended to control knowledge of science so that the results would be looked at as miracles of their god. The biblical wise men or Magi simply used stars to navigate the desert at night (astronomy). Same could be said about medical miracles in the bible. The problem was that people outside the faith also knew about science.
The bible uses words derived from pharmakon (a drug, i.e. spell-giving potion), pharmakeia (female) and pharmakeus (male). But seeing that the results are not from those of the faith they claim it to be acts of evil. That instead of healer, they are poisoners. Odd thing is that science can also explain the plagues of Egypt. Funny thing is, when these acts of science are done to kill, they are miracles of god.
When most people vision a witch, they picture a woman mixing ingredients in a large pot (cauldron) and boiling it down to make medicine (potion). Just because they worked their science outside of the religion they were demonized as witches.
Though they don't technically worship the devil, I do think it is funny how they used a term that associated them to devil worship (witchcraft) with their namesake (wicca).
Other claims of mystical power, i.e. spells, are just taking advantage of the subconscious.
Example: A love spell. A person who believes in witchcraft may pay someone who claims to have mystical powers to cast a love spell. As a result, they may feel that love is coming and may look for signs of it. They pay closer attention to the actions of others. Because they are subconsciously looking at others for longer, others may take this as a sign of affection or flirting. This could cause them to react in a subconscious manner as well such as smiling back. These subconscious actions would likely increase and because the person who purchased the spell believes it to be working makes them not only believe that the other is falling in love but that it is a result of mystical forces.
For wiccans who claim that spells are real. I have a simple way to prove it. Cast a spell on me that makes me believe in witchcraft. To the best of my knowledge it would not break any of the rules.
1) Do no harm: No harm would be done.
2) Do not cast a spell without their permission: I am asking you to cast the spell so giving permission.
3) Be wary of Karma or it will be returned upon you three fold: If it does return to you, then it would just make you believe in it three times as much. Still no issue.
The only issue I can see is that doubt can kill a spell. Not your doubt but mine. Because I know there is no such thing, I am not subject to the subliminal response. If witchcraft actually has power, then my belief in it should not matter.
The devil is simply not apart of our religion just like the christian god. How could we be worshiping something without knowing it? If you assume that then you must assume Hindus, or any other religion for that matter worships him as well. I believe giving a name to evil is giving it power, in my religion there is no ultimate evil.
Devil is evil taken form. You give it a name, you give it a story, and voila you've given birth to your devil/evil being. As a fellow wiccan I must inform you that in our religion there is no darkness and there is no evil. We're peaceful and intune with the earth and our Goddess. The only evil that we see and know about is man itself. And let me assure you we don't worship man.