Replace Bonucci with Chiellini in this context and tell me I'm wrong.
If you're suggesting people will always want a good attacker over a good defender then that's obviously because football fans are often quite stupid.
But isn't that true? Attackers are the stars of the game, every other position unfortunately is considered less glamourous and treated like a supporting cast even though it's those positions that are more often than not the positions that keep a game together.
To answer your question about Chiellini, I would make the trade between him and Isco as well. I don't get why Bonucci fans think he is being crucified. Make no mistake, he was one of the most important pieces of the Juve puzzle last season, so I don't think people would blindly trade him as part of just about any move.
This one rumour if it's anywhere close to being true, would be a hard one to miss out on though given how Allegri is setting up the team next season. Rather Bonnucci be sacrificed than Vidal or Pogba in my view, and I say this as a fan of Bon Bon this past season.