Who dictates what’s stupid? Where does the sanity end and crazy name start?

Sanity ends when the name has an objectively high likelihood of causing the child harm, or otherwise severely hindering them in life. For example, naming your child “Hitler”, or “<insert slur of choice>” is objectively likely to be harmful to them. Likewise, naming them “Helicopter” or “Rollercoaster” is very likely to set them back in life through childhood bullying.

Who dictates this? In all countries I’m aware of that have laws around this: A government body of some kind.