Many common objections to utilitarianism -- e.g. cases involving unexperienced harms or sadistic majorities -- are really objections to a particular theory of the good, rather than to the core idea that we ought to promote the impartial good. So when faced with such objections, it's worth asking not just whether the action seems wrong, but whether the outcome is really desirable in the first place. If not, the consequentialist has a simple response: the act is indeed wrong, precisely because it doesn't maximize what's (genuinely) good.
Consider the case of the perverted doctor who secretly molests his patients while they're unconscious. This seems wrong, even if doesn't cause anyone to experience suffering. But, more than that, it also seems like a bad outcome (in particular, it seems bad for the molested patient). Not only did the doctor make an immoral decision, but he brought about a worse state of the world. The upshot of the example is that there are certain things we consider undesirable, things we don't want to happen, whether or not we learn of them. A plausible theory of the good will need to accommodate this, which rules out value hedonism, but leaves untouched the core of utilitarianism (i.e. impartial welfarist consequentialism).
A slightly trickier case is the "KKK world", where an overwhelming majority of the population consists of racists who derive immense sadistic pleasure from oppressing the minority. Even if oppressive actions maximize both net pleasure and preference satisfaction, they still seem clearly wrong. I agree with this judgment, but again, it also seems like a bad outcome. We can establish this most clearly by noting that it would still seem bad even if the outcome were the result of natural events rather than human agency. That is, suppose a black guy is struck by lightning, bringing malicious happiness to millions of racists. There are no "wrong actions" here, for the simple reason that there are no actions at all. Nonetheless, it doesn't seem like a good way for things to turn out. The upshot, I take it, is that there's no value (perhaps even disvalue) in sadistic or malicious "pleasures" of this sort.
Is there a sure-fire way to diagnose whether one's intuitive response to such a scenario represents an intuitive rejection of consequentialism proper, or just a particular axiology? I'm not sure. A good heuristic -- sufficient but not necessary to establish intuitive disvalue -- is to try to 'naturalize' the event (as in the previous paragraph) and see whether the intuitive repugnance remains. But it may be difficult to do this with some cases. For example, in the doctor case we can imagine a version where he 'touches' the patient as a result of a muscular spasm rather than a choice, but this no longer seems nearly as bad. Sometimes it is precisely the vicious or inconsiderate exercise of agency that contributes to the disvalue of the outcome.
Once consequentialists build the intrinsic disvalue of vicious action into their axiology, we need a more sophisticated test to distinguish them from deontologists (and hence to distinguish genuinely deontological intuitions from mere axiology-refining intuitions). At this point we may turn to agent-neutrality. For while a consequentialist may be concerned to prevent vicious actions, he is ultimately no more concerned with his own actions than with other people's. He will thus consider it worthwhile to perform a single intrinsically bad action himself if this prevents multiple similarly bad actions from others. I take the essence of deontology, by contrast, to be the idea that there are side constraints on action that we simply shouldn't violate, not even to prevent more such violations in future. This is what the deontologist really needs to establish. But of course that isn't nearly as intuitive as the axiological claim that (e.g.) value hedonism is false.