Aside from the fact the federal government cannot pass amendments without the state, this proposed amendment is not about morality, it is about stopping the unelected courts from enforcing their percieved morality on the people of the state.
If the citizens of state X want to have homosexual marriages, this amendment would not stop them. But if judge y decides that homosexual marriage should be the law of the land regardless of the desires of the people, this amendment would stop him. Likewise, if the people in state x make homosexual marriage the law of thier state, this amendment would prevent an overzelous religious radical judge from overturning the will of the people in state x because of his percieved morality.
The amendment would protect the will of the people and the right of the state.