Also,the material was destined to 7-10 year olds not adolescents.
That is just how public education works.
Like imagine if a flat earther parent complained that schools are teaching children that the earth is round and demanded it being removed.
Public schools will teach what society at large deems neccesary to be taught, if you don't want that then educate your children yourself.
We live in an era where homophobia and other prejudices are trying to be eliminated and teaching children about other sexualities is part of that. So yes maybe it is a war on a pre-established culture, but consider, is the part of that culture being phased out even worth being kept then?
Like if you had country where slavery was the norm, then society started to change so that children are being taught that is slavery is wrong, that would also be a war on culture, but one that's ultimately for the better.