But I really don't see an utopia in which, for a bit more of fun of a single person, the whole humanity will lose something like one of the last Stardivarii.

I suppose this depends on whether one is allowed to own a Stradivarius. If I own a Stradivarius, I can indeed use it to row a boat, or for target practice, or to start a campfire. If this is Ishtar's (or the villain's) Stradivarius, then they can play this game with it. This changes if you're not allowed to own things, or some kinds of things, in utopia.