Circumscribing circles are optional. For involved mystic symbolism, the triangle is a rather dull figure. I agree strongly that offensive speech should be completely protected. There probably would have been more complaints if the cross or Star of David had been used. That doesn't make the complaints right.
History shows that.
On the subject of invocations, etc. The book also describes several rituals, including one to invoke Elemental Spirits. That particular ritual did not include any circle, triangle, or pentagram, but there were several citations, including A.E.Waite, a famed 19th century occultist. I don't remember whether the pentacle was to be upright or inverted, or whether it was of particular importance, in Waite's book. This phenomenon is quite common on Usenet netnews.