HOWEVER, online I've seen name change beliefs within fundamentalist circles which concern me personally
Name changing for quite a few of these families (not saying it's every family, because obviously it's not) is not purely a 'parental desire' - it's also a religious issue. It harks right back to God renaming Abram and Sarai. He also renamed Jacob as Israel. Jesus naming Simon as Peter. Saul became Paul. THAT is one of the major reasons some fundamentalist families will give for renaming their new children (even the teenagers. Without asking their consent). Because some people in the Bible whose lives changed course in very significant ways were renamed to signify this. Some parents see this as a similar situation for their children - they are gaining a real family, and the true religion, and hence a new name is a very important symbol of this transition (if i remember correctly from reading fundamentalist parents blogs)
Additionally a smaller number of families will feel that God Himself has chosen the name in advance. I have genuinely read an adoptive mums story of how God spoke to her and told her the name of her future child. Years before said child was adopted.
Obviously this makes the name changing issue even more complicated than before. It also puts the child in a very difficult position.
When I gave my son a new first name at the age of just turned 2, I accepted that he may wish at a later age to be called by his original first name instead. And that was okay by me. I had very good reasons for the name change, but I also accepted completely the importance his original first name might have to him later on. Right now in reality he has desire whatsever to go by his original first name, completely the opposite in fact, but in an alternate universe would I have felt personally rejected if he chose to go by his birth name? No. Sad, yes. Completely rejected, no.
But these children? If they are accepting (a fundamentalist branch of) Christianity as their new religion, if their parents are telling them that their new name came directly from God Himself, or has deep religious significance, how can they feel able to turn down a new name, or go back to being their birth name? It might be felt not only as a rejection of parental authority, a rejection of a parents love, but ALSO as partly a rejection of the Bible, of God, of Christianity. And in fundamentalist circles, that's as bad as it gets. And if the child fully believes in it themselves, would they feel able to revert to their original name even if deep down they wanted to?
So that's the one more concerning facet of name changing for me