That is more of an argument involving the implementation of tags in general within the federation. But to answer your question:
Let's say a group of people were to make a post on Mastodon with the tag #girls_night. How will all instances agree on the tag being correct?
The simple answer is they won't. If a tag is contentious, it will be like any other drama between instances.
It's the same for implementing tag hierarchy. Let's say there is a default setup. Then if a tag or a tree of tags is contentious, each instance can include or exclude as they see fit.
This place is more techy, but please don't assume. I have no idea what you're arguing for.