Singer is, according to some, the most influential philosopher alive today. He's also one of the few who are consistently generating new and interesting ideas. I find that with intellectuals of his ilk, even if you disagree with every word they've said, exposure is still worthwhile because in listening to them and disagreeing with them, you generate new ideas of your own that might not otherwise have occurred to you. So I can't recommend him strongly enough.
To put some meat on the bone, Singer's contribution to our discussion that I think is particularly valuable is his inclusion of animals empirically determined to be self-aware within the definition of "person." The consequent attribution of "human" rights to self-aware animals changes the moral paradigm substantially. If one is to adopt even a vestige of a deontological or rights based framework, adopting Singer's approach means re-thinking swathes of public policy, corporate regulation, and even personal choices. It is more or less accepted by this point, I think, that both dolphins and orcas show some or most elements of self-awareness, dolphins, for instance having famously done very well on the
mirror test.
As I understand it, and please correct me if I'm mistaken, you are describing the classic utilitarian/deontological "rights" based dichotomy and trying to fit the issue of orca captivity within that paradigm. This is to some extent the entrance to the rabbit hole down which many animal rights discussions disappear. I suggest, though, that we have no incentive to commit to one side or another and instead can identify elements of both approaches in commentators who pretend to be wholly committed to one side. Singer, for instance, despite his radical exclusion of some humans from sapience delimited personhood, goes so far as to say that he would not exclude the use of sapient animals for medical tests for the benefit of humans. That, to me, screams consequentialist thinking. Most of your committed neo-utilitarians, on the other hand, will blanche if you suggest to them that animal torture without any medical benefit must be acceptable for them given that it contributes to the happiness of the torturer but detracts from no "person's" happiness, especially if it is never discovered.
Now of course we could think of an even dozen counter-arguments to both of the above objections if we wanted to, but this does not change the fact that there are some principles governing our relationship with animals, particularly self-aware animals, which appear close to inviolate, whereas most appear to some degree contingent. Applying this to the situation at hand, we consider whether orca captivity at Sea World infringes on any inviolable or quasi-inviolable principles, or alternatively whether there is a consquentialist argument which justifies the demonstrable psychological damage inflicted on the animals which I alluded to earlier. The fact that the animals are being used to entertain with antics contrary to any behavior to which they are naturally inclined, rather than being provided to allow people who would otherwise never experience these incredible animals, also needs to be taken into account.
I think we can agree that this is an issue on which reasonable people can differ.