Sorry, I've seen your post only now, so my reply is a bit late. I think we mostly agree, but it appears to me that you might not be fully aware of the magnitude of the metaethical problem and persistent disagreement about them. To give you an example from formal ethics, according to Temkin's Spectrum arguments strict "better than" comparisons are not transitive. Some authors agree with him, others disagree. Some want to give up completeness instead of transitivity, others opt for lexicographic value hierarchies. Others deny having the intuitions and argue for the status quo. Even this one simple issue has far-reaching normative consequences, though. If Temkin is right, then even if we all agreed to be classical utilitarians, the position would be infeasible and any account based on utility functions would be wrong from the start.

If at all, we could try to implement conforming with systems of laws as hard constraints, so at least robots would not openly break the law. The rest of moral behavior could then be learned. Or, so one might think. However, even that is not possible. It is well-known from the philosophy of law that systems of law are not contradiction free. There are conflicts between opposing laws. This is studied in normative systems research and there are solution to it (essentially, by logicians in the computer science tradition). However, these require some form of defeasible rules, and among the myriad of nonmonotonic logics that can express some form of nonmonotonic reasoning, not a single one has a normative justification. So again, as long as human standards are not coherent enough, it's going to be impossible to make a machine conform to them in a way that is satisfying.

Related to that, I believe there are two main issues that you haven't addressed in your post:

1. Different standards for blame and accountability: The standards for blame and correctness of decision making are completely different between machines and humans. Even very intelligent AI would be judged at much higher standards as humans. I simply don't believe that we would accept robots that commit murder, just as long as they commit murder less often than humans. By the same token, we do expect machines to make substantially less errors, and in certain areas would not allow errors at all. So it's not just about teaching them to follow human ethical standards - they need to excel at this and may not break the law. However, as I tried to show with the above examples, we don't know and agree on our own standards well enough to be able to start making sure AI fulfills these high expectations. There is also a much higher need for transparency of decision making for machines than from humans. An idiot driver is an idiot driver. If a car is driving like an idiot by itself, however, you'd expect to be able to at least retrospectively find out why it did what it did.

2. The political dimension: Laws are the result of a political process. Appointed judges resolve potential conflicts between laws and interpret them. More broadly, whatever standards we expect AIs to fulfill hinges on ethical positions and personal preferences. It can ultimately only be decided as the outcome of a political process as well. For example, a safe a self-driving car needs to be, how it makes decisions (e.g. "Should I try to save my driver or save the pedestrian, or not have any priority at all?"), and which standards it needs to fulfill is up for debate. That is not decided by moral philosophers. It needs to be decided by the publicly accountable, democratically elected representatives of the people. The idea of teaching a machine to behave morally is fine, but there are also strict standards of safety and transparency it has to fulfill. This is a political problem and can only be solved in a broader context, within the debate of how much AI should be allowed at all. For example, should AI judge your creditworthiness? If so, what false positive rate would be tolerate? I believe using AI for such purposes should be strictly prohibited. Others disagree - I'm sure AI is already used for that. Such issues can only be resolved politically.

I considered your post a bit naive, because you omitted these two crucial issues, the higher standards we expect from AI, and the political dimension. Other than that, I agree with much of what you've said.