If an artist X publicly says he was inspired by band Y, or if a writer, specialist of related genre or band X says so, and if editors agree, then we can just create a relationships.
Copyright cases have and will happen with or without such relationships in MB.
To me, that’s totally unrelated.
Of course it is, but they are plenty of subjective informations around that are still useful, right?
For example, Metal Archives has lyrical themes for bands, I guess that’s very subjective, but that’s clearly a nice addition to genres (in the same genre, you can have various lyrical themes), as it helps to define the band.
Wikipedia is also listing lyrical themes in their articles (example: https://en.wikipedia.org/wiki/Pink_Floyd#Lyrical_themes).
It’s more about the process, and we clearly do that already with genres.
As other data, any relationships should be sourced, and voted.
Example for sources related to influences: https://en.wikipedia.org/wiki/Pink_Floyd#cite_note-425
Another partially subjective thing Wikipedia is listing is Associated Acts (https://en.wikipedia.org/wiki/Template:Infobox_musical_artist#associated_acts)
We don’t have those (as is), but they exist on Wikipedia because users/editors found this kind of information useful.
AFAIK, MusicBrainz database is made by people for people, and as a music fan, an editor, and a human I think knowing that artist X was influenced by artist Y is a useful information, hence the ticket.
One may disagree about the usefulness, but no one is forced to use or edit this data anyway.
Same goes for genres.
Also to be honest, we have plenty of perfectly objective data in the database that is totally useless to most users.
As an example, I don’t care if artist X is married to artist Y, but perhaps if those artists are musically influencing each other, or writing music together, which may not be the case at all.
Though this relationships exists in the database, perhaps because some people found it useful.
I don’t ask to remove such “married to” relationships, I’m perfectly fine with it, I even added some of those relationships.
But if you asked me to choose between “married to” or “influenced by” relationships, in the context of a database dedicated to music, I would have chosen the latter right away, just because the former is unrelated to music.