This has nothing to do with right or wrong, it is purely a choice of interest.
He can only make the last effort to try, using all his abilities, as no matter what, even the weakest Daoist Monarch and True Immortal are not on the same position; one is a collaborator, and the other, a vassal, the rewards they receive are drastically different, making it worth their while to wager everything for one last attempt.
It is not just True Martial Emperor who has made such a judgment, wanting to make the final attempt. Every strong being standing in the True Immortal Sixth Layer among the heavens and earth thinks and acts the same.
After all, compared to the strong beings below the True Immortal Sixth Layer, even if they clearly understand the situation, unless their luck is incredibly good, it is impossible for them to ascend two layers in a short time and become Daoist Monarchs, which means they have no chance at all.