If you're arguing for lack of free will then I'd agree but it makes the whole point moot. A moral theory is generally independent of any specific persons so not sure why that's relevant? Furthermore you absolutely could reduce a persons actions to an algorithm just maybe a complicated one.

If you can describe a precise way of determining what is most moral or even just more moral of 2 choices then you have an algorithm. If it is not precisely defined then it's ambiguous in which case it's not justified I'd argue? Since you haven't even defined what it even is.