Fan I'll be honest with you, there was one single big mistake the school/HT/DHT made, and had they avoided this mistake most, if not all, of this mess would've been avoided. Now I don't know the full S.P. on this and I may be wrong, but they didn't hold any parents consultation meeting BEFOREHAND, discussing what they were going to introduce, why they were introducing it, how they were going to deliver it, what was going to be taught and at what age. Then listened to parents concerns and had those difficult conversations BEFOREHAND and hopefully come to a suitable compromise which everyone or at least the vast majority would have agreed to.
This usually involves discussions with the PTFA but imo on such a sensitive issue the school could've developed a wider Parent/Community group and then a separate parents meeting if necessary. I say this because I've personally had to manage sensitive issues such as Ramadan during hot summer months where young children were at risk, as well as residential trips which were also a tricky subject. These were situations that the schools were already experiencing difficulty with, but if you reach out before the event and have a discussion I've found most misunderstandings are resolved without fuss - misunderstandings between perceptions of what is being introduced as well as misunderstandings on perceptions of the intentions of the school.
The way the school appears to have gone about this was all wrong imo, by the senior leadership team. It comes across as either incompetence or a sense of "we're going to get resistance but fck it we're right" attitude. I wonder what kind of school/parent relationship existed in the first place. Seems like there was mistrust to begin with and that in schools is, more often than not, borne out of a lack of communication.