The Samaritans don't recognize the nationality of Israel at all, nationally, they were still considered enemies. Thus, their participation in the Torah is only out of their desire to accrue its potential reward, or, for their elite, because they recognize its truth. Thus, the words of Chaza"l are very precise, in the opinion which gives the Samaritans the benefit of the doubt that they did not convert simply out of fear of lions (Gerei Arayot), says that they are 'Converts of Truth' (Gerei Emet), which is not the usual term for Chaza"l who generally use 'Righteous Converts' (Gerei Tzedek). Meaning, that 'tedek' (justice) refers to the whole community of Israel, whose basic purpose is to bring eternal justice to mankind. And he who has no everlasting connection ('yad va-shem') with the God of Israel, though he may recognize only the grandeur of the Torah as reflected in its aspects of truth, can only be called a 'convert of truth', but not a 'convert of justice'.
In other words, 2 converts: one says he joined because he was convinced that the Torah is God's revealed Truth to man, the other says he liked Jewish values and how they express themselves in the way Jews treat others.
R' Kook is saying that the latter is the better reason. Amazing.