You claim that just as the laws of physics operate as universal so should moral reasoning. However many laws of physics are relative. For example, the speed of light is 299,792,458 metres per second...in a vacuum. When light passes through a transparent or translucent material it is slower. So the speed to light is realtive to it's medium. Newton's laws of motion, like say the first (the law of inertia), is specifically predicated on a neutral inertial fram of reference. So, for example, a small object within an excelerating body does not abide by this law of motion. Special relativity and extreme gravitation also operate contra Newton's laws. The current forces of nature (the four fundamental forces) did not operate as they do now during plank time.
You say, "No moral theory can be valid if it argues that a certain action is
right in Syria, but wrong in San Francisco. It cannot say that Person A
must do X, but Person B must never do X. It cannot say that what was
wrong yesterday is right today or vice versa." So wouldn't the above relativity of those physical laws seem in direct contradiction to this sentece.
Does universality work with the generalized and unconditional rules you lay out? Put it another way, isn't everything relative at a simple level and made absolute by relation. For example, the statement "if I drop this rock it will fall" is incomplete, thus it's truth is relative. The statement, "if I drop this rock while standing on a body with a minimal gravitation of X, it will fall" is an absolute. The statement that the a car is large has no truth value. The statement, the car is large in comparison to me has truth value. The idesa of hot/cold, soft/hard, simple/complex, and so on and so forth are each relational propositions. Now of course we use context to silently fill in the blanks during everyday speech, but should not philosophical/ontological propositions be as accurate as possible?
I'm not challenging or criticizing universality, at this point, but only seeking clarification of how the concept functions in light of the hypothesis that truth value comes from explicit relations?