I think you have done a pretty good job of discussing the implications of ethical relativism. I would summarize what you have said as follows:

• Neither the theory of cultural relativism nor the theory of ethical relativism logically entails a moral principle of tolerance. Nor does either entail that people in one culture should not criticize nor interfere with the actions of people in another culture. Of course, there may be good reasons for for tolerance and so forth, but that is a different question.
• The theory of ethical relativism does not imply that moral judgments or principles are arbitrary or that "anything goes" in morals.
• The theory of ethical relativism does not imply that there are no rational methods for resolving moral disputes. There are rational methods in some cases, although not necessarily all cases.
• Some of you described a holistic theory of what it is to have good reasons to accept a set of moral principles. We could call these principles "moral knowledge," but that might mislead people. It may be better to speak of "having good reasons to accept" certain principles. We could also describe this approach as a "coherence theory of justification." It relies on making our considered moral judgments and all available knowledge consistent with proposed moral principles by adjusting any of the many elements in the mixture.
• Some of you also pointed out that this coherence approach is not guaranteed to yield a single set of moral principles. Nor is it guaranteed to settle all ethical disputes. As John pointed out, rational argument comes to an end. It has its limits. If we accept ethical relativism, we must accept those limits as part of the nature of the ethical reasoning process.