Except the kid is not YOUR OWN child, in the meaning of possession. You are the custodian to the child, not the owner. The child basically is owned by itself and you are (usually) allowed to take care of it and lead it on that way.
And there are tons of laws that forbid abusing childs. Like you can't hit them, shake them. In the USA they perhaps have a law that you can't put them in a microwave, I dunno.
And the laws in the european countries that forbid silly names are usually not restrict your "owners rights", but to protect the kid. In Germany, I mean, over here they forbid that people called their kid "Rumpelstilzchen", the name of an imp/goblin in a very well know fairy tale. If the parents would have come through I expect that the kid would have ridiculed in school and outside quite a lot. Other kids can be cruel ... and even the odd mindless adult.
Actual names that german parents wanted for their kids, but that weren't granted: Bierstübl, Borussia, Crazy Horse, Gastritis, Grammophon, Januar, Joghurt, Kirsche, Liebknecht, McDonald, Millenium, Möhre, Pfefferminze, Pilulla, Porsche, Rosenherz, Rumpelstilzchen, Satan, Schmitz, Schnucki, Schröder, Seerose, Sputnik, Störenfried, Rasputin, Verleihnix, Waldmeister, Whisky, Woodstock
Some have outright negative connotation (Satan, Störenfried, Rumpelstilzchen), others are just extremely uncommon and thus standing out. For example, in Germany we don't name girls about other things like Melody, Crystal, Daisy, Faith, Grace, Haven, Hazel, Amber, etc. So if you name your kid after a product or a thing, e.g. Porsche, Kirsche or Joghurt, then it will draw the wrath of the other kids onto itself.
And THAT is the reason the authorities don't allow a name. It's not about unusualness alone. A lot of unusual first names were the parents could show "Esenosarumensemwonken is a first name in Nigeria" go through.