This is ridiculous, and it seems obvious to me to be a reaction to the pentacle being a symbol many Christians associate with Satanism or other "evil" religions. It's a simple numbers game--they'll offend fewer Wiccans by not putting the symbol on the tombstones than they will Christians by putting it there.
I do find it amusing that on the
listing of approved symbols, they have a few that may have only a few thousand adherents in the US, such as KONKO-KYO FAITH, a sect of Shinto (which does not have an approved symbol) or IZUMO TAISHAKYO MISSION OF HAWAII, also with only a few thousand adherents.
The difference, of course, is that if you put a symbol for a small Japanese religion with a tiny number of American adherents on a tombstone, nobody is going to blink; a pentacle pisses off the wrong people. This doesn't make catering to their ignorance any better.
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So the Christians and the Pagans sat together at the table
Finding faith and common ground the best that they were able
Lighting trees in darkness, learning new ways from the old,
And making sense of history and drawing warmth out of the cold.
Dar Williams, "The Christians and the Pagans"