From most reports, IU fans acted horribly in Bloomington.
That said, it's not the real reason UK won't play there. Or at least not the primary reason.
1. As he's stated, Cal doesn't like playing friends. Crean is among his best friends. If he can get away with it, he won't play Crean. (Crean likely feels the same way.)
2. Neutral court games are better preparation than home-and-homes for the NCAA Tournament. That's Cal's focus every year. (It'll be Crean's too, IMO.) What good does it do to play in front of 14,000 rabid fans who could very well injure a star player if they storm the court? (Darius Miller and Terrence Jones came awfully close last season to getting stomped. DeMarcus Cousins came closer three years ago at South Carolina, IIRC, when a fan challenged him to a fight.)
3. A December game (and especially a loss) might hurt freshmen psyches. It affected the 2012 team, though they eventually got mad and it helped them win later. A less mentally tough team might have been devastated and never recovered.
4. An almost guaranteed win against a (barely) Top 100 RPI team or a glorified practice against Southwest Directional State University mean just as much to Cal as does a game against IU. He's not into measuring sticks. Especially that early in the season. He claims they mean nothing to him, as he's looking at what can make his teams play best in March.
5. Cal is at the point where his RPI isn't going to mean much with the NCAA. His teams are always going to be ranked high enough pre-season to stick close to the top 15 and his conference is strong enough to keep him in an RPI range that won't hurt him. In short, a victory doesn't mean much mathematically.
6. Every game is on TV anyway. Almost every weekend is a national game already. Why risk the loss on national TV for a win that means so little? His recruiting is monster-ish-- among the best runs CBB has seen since UCLA and Sam Gilbert-- ummm, I mean John Wooden. Why take the risk of adding to IU's reputation while simultaneously taking away from your own? From this year on, Crean and Calipari are likely to go after pretty much the same kids.