If you agree completely, why don’t you use a non-white dress? Respectful attire is all that is needed. Anything more is window-dressing.
Let’s put things in perspective.
It’s a diminshing of the seriousness of “rights” to call wanting to wear a white dress for First Holy Communion a “right.”
There is a right to life, liberty, and the pursuit of happiness.
Wanting to wear a white dress is a preference. It has no bearing on the sacrament itself. It is a symbol and nothing more, and not even an important one. I’ll wager that the boys in this First Communion class are just as pure as the girls, and I will bet that none will be wearing white suits.
What is wrong with deferring to the priest’s wishes on this matter? Is that option on the table?
This is a society in which people want what they want, regardless of the lack of magnitude of the situation. However, this is just not worth the fight.
What your daughter, and everyone else in the First Communion class and in the parish, will remember is the discord of this event, not the beauty of the sacrament; the beauty which is being in communion with Christ, partaking of His Body and Blood which gives us the grace to take His teachings of love your neighbor to the world.