Hayes was a complicated figure by the standards of his time and by ours. He was a slaveholder’s contemporary who made a ruling against slavery’s extension. He was a Missouri-born jurist in a recently American city whose legal culture was still forming, and he used the flexibility of that forming culture to reach an outcome that the formal legal structure might have foreclosed.
The question of why he ruled as he did is not fully answerable from the surviving record. He may have been motivated by a principled commitment to California’s constitutional prohibition on slavery. He may have been troubled by the specific circumstances of the case, particularly Smith’s attempt to remove people to a slave state from a free one. He may have been responsive to the moral claims of Mason and others in her situation in ways that the formal legal structure did not require but that his own judgment endorsed.
What is documented is that he heard the matter in his chambers, that he deliberated for three days, and that he ruled for Mason and her family. The ruling’s reasoning — that the removal was intended to be carried out without the free will and consent of the persons involved, and that those persons could not be said to have voluntarily agreed to anything given the conditions of their relationship with Smith — was careful and defensible. It left open fewer grounds for appeal than a purely emotion-based ruling might have.
Hayes also made the practical connection that placed Mason in the professional network she needed after her emancipation: his introduction to Dr. Griffin was not required by any legal obligation and reflected a form of personal follow-through on the case he had decided. This suggests that his involvement in the matter was not purely formal; he had some sense of ongoing responsibility for the outcome, or at least some concern about the welfare of the people he had freed.