Pity the poor bird that accidentally swallows one of those balloons after it deflates and drops to the earth...
;-)
You are right. Balloons are dangerous for birds, they ingest the pieces, they get tangled with the strings etc. On top, these doves are raised in captivity, they get released in ceremonies, they have no sense of behavior in the wild and they are easy prey to other birds. Cruelty, IMNSHO