I'm speaking in general about religions,not just christianity. If a spell or circle were being used to achieve the desired results by calling on gods or goddesses in a carefully proscribed way,intending to enforce their aid,willing or not,to enforce you will,I would not call that prayer either. I have read the Mists of Avalon. I thought it was a very interesting book,both for her ideas on religion and feminism. I think it helps make witchcraft very attractive as a religion.
Many people object to witchcraft from a religious point of view.
It doesn't fit their beliefs or cultural biases. Others object to it from a scientific point of view because they don't believe in magic.