Let me clarify, since I think I can pinpoint where our misunderstanding occurred. After examining this closely, I think this is a case where we both are right.
Witchcraft is forbidden, because some people believe in it and attempt to use it, and I can fully understand you pointing to this and saying "See, it does exist." But its claims are false. Casting a spell accomplishes absolutely nothing. The only thing an amulet does is make you feel good. In this respect, a working Witchcraft does not exist, which is what I was pointing out.
In the identical way, the prohibitions against idolatry and other gods are there because people BELIEVE in these false gods and worship them. So yes, the PRACTICE of idolatry exists, which I believe is your point. But their belief does not mean that these gods actually exist, nor does the prohibition of idolatry mean that these false gods exist, which is the point I was trying to make.
Consider this a case of "we are both right" and kind of were talking past each other at first.