Well, "hate" is probably too strong a word, but for me it's actually this very thing that everyone else seems so big on, that being the Bruce/Cass fight and the whole "who do you belong to" that bugs me so much. It validates Bruce's treatment of Cass; his crazy-kill-each-other therapy being the only kind of therapy that she'd understand, and the thing that brings her around and gets her back on an even keel... It says "Bruce does understand Cass, he gets her better than anyone and in the end, was the only one of them who had any idea how to act in her best interests and help her out with this." It says "repeating her relationship with Cain with pain as the only effective form of communication is the healthiest thing for her."
Which is already annoying taken in isolation, but when you add to that the fact that Babs is never given a moment of connection with and understanding of Cass or victory over Cass' demons like this, and that all of Bruce's other behavior toward Cass throughout the series is utterly appalling and like, precision custom-designed to most effectively increase her dependence on him and further aggravate her psychoses, while Babs screws up much more infrequently and makes a concerted effort to make Cass healthier and more functional, then this idea that Bruce does get Cass and does do the right thing for her and nobody else really has that ability... it's incredibly creepy and wrong. It justifies his abuse of Cass (after all, him doing something crazy and apparently abusive helped her here), and by implication, dismisses Babs as wrongheaded in her positive behavior (because he's pretty constantly telling her she's doing it wrong when it comes to their co-parenting).
Plus, his questioning of her loyalties here has always seemed a) gratuitous (like she hasn't proven her loyalties a dozen times over), b) a destructive reinforcement of her existing self-esteem issues (like she doesn't kill herself trying to prove herself to him already), and c) sort of adversarial and undermining of Babs (if there's a difference between loyalty to Babs and loyalty to him, that's kind of telling Cass she has to pick a side).
I mean, that she's loyal to the concept of the Bat more than any one person is a very cool Cass moment, but Bruce's behavior and the way the meta-narrative interacts with that behavior leaves a pretty foul taste in my mouth.