Why are ideas any more fragmented than a different form of topic based approach that uses a particular religion as a topic, or the idea of ceremonies as a topic and compares religions.
I can't see why this is any less fragmented than a topic based approach based on ethical issues, nor why this is fundamentally a problem.
If you deal with ethics in a 'case study' format, one will tend to look at the case in point and decide on what one's response should be within the 'vacuum' of that single case or set of cases. This can lead to creating ethical codes that have this segmentation built into the process. I prefer to teach ethical principles and then look at how they apply to individual cases. For instance, how does war impact on the idea that one should not kill? Or is taking perfectly good food from a trash bin outside a supermarket to help feed the homeless stealing or not?
I got the impression that you would like to see the context be the starting point and an ethical principle be developed from it. If I've misunderstood you, my apologies.
Well I guess that you like me have actually studies and taught ethics, so actually have some experience.
So on that basis, yes there are different approaches, but I don't see that one is fundamentally better than the other.
Personally with a group of students I first like to explore some case studies and get the students to give their 'gut' reaction to right and wrong within the cases. I do this for a number of reasons:
1. It is easier I think for a student to consider their own reaction to abortion (for the sake of arguments) or the practical examples you used rather than start by dry ethical theory and then to begin to explore why people react in a particular manner.
2. When done in a confidential and anonymised manner (which is what I do) it allows the range of view to be revealed within the group. This is helpful as it support the notion that students should be mindful that the person next to them might disagree, perhaps quite radically, and to respect the group so to speak. Further to recognise that there are a range of opinions and when legislators etc try to make decisions they actually can't decide on the basis of the consensus view, because often there isn't one.
3. Many people develop an approach to ethics with is inherently 'hybrid' a bit religious upbringing-driven, a little bit golden rule humanism, a touch of consequentialism etc etc. Few of us adopt a pure ethical theory and apply is consistently.
Only having done that do I tend to introduce classical ethical theories - why, because I find that students tend to engage with them much better when considered in the context of their own views on particular cases. Further it helps students to understand the limits of their adherence to a particular ethical approach.
I find this works pretty well. Perhaps you do it differently and that's fine if it works for you. But I guess to my mind ethics (certainly practical ethics) is about exploring individual views on topics in the context of ethical theory. It isn't about learning an ethical theory (even less so learning the 'correct' ethical theory) and then practicing it by applying it to situations.
Where I do lean toward the 'learn the theory and then apply it' approach is only where ethical practice is legally codified - a good example being the requirement for consent in medical ethics.