Your opinion of the issue is irrelevant. It IS a divisive issue, according to the parents of those children. That is why there was a complaint (or many. I'm not clear on that).
People who work for the taxpayers are accountable to the taxpayers. People who work for schools are accountable to those children's parents. You and I don't have to agree with the parents. But it seems reasonable to refrain from discussing subjects about which there is much disagreement. Teachers and bus drivers work for the parents.
Some parents are crack-pots whose opinions should be ignored. This is done quite commonly, and is nothing new. While I am quite the supporter of parental rights, there need to be some reasonable limits. To demonstrate with an extreme example: if I were to suddenly decide that mathematics was a tool of satan, and I did not want anyone around my children talking about anything remotetly connected with mathematics...then what should the school about this?
The parents in question seem to have objections that are manifestly ridiculous.