An ethical question for materialsit

[Terrapin Station]

Physical forces have nothing at all to do with inter subjective moral consensus

Nonsense--physical stuff and physical "forces" are all there is.

[Conde Lucanor]

How any ethical system can be defined under materialism when everything is simply the result of cause and effect. How possibly we can define right from wrong based on cause and effect?

Is there anything that is not simply the result of cause and effect?

That was not my point. The problem is how you can define an ethical system based on cause and effect.

If that was the point, the problem is not then related to materialism only, but to anything else that you can devise outside materialism, too. Unless, of course, if there were something else where cause and effect does not apply.