This 'only biological, no social interference' stance is wrong as it implies that Archer has to give the cure if the Valakians wage war against the Menk or put them into concentration camps.
Neither of which were actually happening, BTW.
In any case: Curing disease trumps all. If you have the cure for some disease, and you are confronted with people suffering from that disease who ask you to help them (which would automatically render the Prime Directive inapplicable, as you are allowed to help anyone who ASKS), you are obligated, under all circumstances, to provide it. There can be no circumstance under which it is ever ethical to refuse to cure someone if you have the power to do it.