Maybe serving could lead to a desire to be nun. I’m sure the girls have been or will be catechized to know they can not be priests.
Personally, I think there isn’t a theological reason girls can’t serve. However, I do think that parishes are missing an opportunity when they do.
I see some more traditional parishes and ones dedicated to the EF have all boy altar servers PLUS Legion of Mary for girls.
In these parishes, the boys don’t just serve. They go through a “training program” which teaches them about the GIRM, the liturgy, pray the hours (when they are there), etc., plus they learn what it’s like to be a priest. Take tours of a seminary, etc. Those altar server programs are really ran like seminary prep programs.
Meanwhile, the girls go participate in Legion of Mary (a youth version). Also pray the hours (when there), spend time in adoration, pray the Rosary for the parish and all the intentions of the parishioners, visit convents, do community service, etc. Those programs are really run like a nun’s preparation program. They also often sit together at Mass, wearing their veil and sash and lead Marian prayers before and/or after Mass.
So while I think that altar girls are not theologically wrong, I think we are totally missing the boat. We should really be treating the altar boy program as a priest recruitment and preparatory program, while offering a girls Legion of Mary prayer group (or another group) which really is a nun preparatory program.
Obviously, we wouldn’t want the two programs to be limited to those who are only interested in becoming a priest or nun, but really push it in a passive way. If the boys don’t become priest, perhaps they will become Deacons, apologists, evangelists, and/or catechists. Same with the girls (mins the ordained part). But most importantly, hopefully they will become better evangelized and catechized and can lead the way to strengthen the Faith of the next generation and their children.
May The Lord grant us the wisdom, vision, “knowhow” and fortitude to strengthen the Faith. Amen.