@gummyfunny,
My opinion - it is none of their business - a parent should try to do what they feel is best for their child.
My thoughts on why parents are trying to petition against it...there are some parents that will redshirt their child to give them an advantage over the children in their grade either for academics or even athletics. I know my daughter plays basketball -- she is in middle school and basketball competitions are usually based on grade not age. There are some girls that are in her grade on other teams that are older but in her grade. Teams grab these girls - so yes it really happens as crazy as it sounds. The thing is as you get into high school these advantages get smaller and smaller so in the long term there isn't that much if any advantage.
So I don't think these parents are being selfish, just probably looking out for their own children's best interest and to put them on a level playing field (pun intended). They probably think that parents that redshirt are being selfish.
Overall though - I don't think it is abused that much and I would think it best to leave up to the parents - maybe if you are concerned about your son you can talk with the teachers/principal/school district to see if you can get an exception if this does occur. If you have a good reason like your child is immature (not unusual for boys) and on the younger side of the age cutoff - even get some support from your child's doctor.