Until recently, the pentagram was a Christian symbol.
The five points of the pentagram represented the five wounds of Christ on the Cross.
Not quite sure how it got transformed; I speculate because the symbol of Christ was used to for "protection" --- and those who most needed protection were those who dabbled in things they ought not have --- it got a bad rap.
The pentagram was used with astrological or religions meaning long before Christianity, and has been used by many cultures since. I'm not sure why Christians discarded it.
I believe it has to do with the belief that by turning something holy upside down, (inverted pentagram) that it somehow is opposite and therefore, evil.
The pentagram has always been an important symbol.
It also represents the human body: head, arms, legs.