They’re just upset that they can’t play their power mind games on the people who aren’t attending.
This seems like an invented problem, invented by someone with too much time on their hands.
I am all in favor of parental involvement in the schools, and with their kids education. These particular parents are doing something right, if their kids are doing well in school and not getting into trouble.
Bingo! Right on! The indoctrination starts with the kids and then "trickles up" to the parents.