What is Dimsdale’s argument?

Dimeedale argues that it might be better for Hester's accomplice if she did in fact name him so....

"I charge thee to speak out the name of thy fellow-sinner and fellow-sufferer! Be not silent from any mistaken pity and tenderness for him; for, believe me, Hester, though he were to step down from a high place, and stand there beside thee, on thy pedestal of shame, yet better were it so than to hide a guilty heart through life. What can thy silence do for him, except it tempt him—yea, compel him, as it were—to add hypocrisy to sin? Heaven hath granted thee an open ignominy, that thereby thou mayest work out an open triumph over the evil within thee and the sorrow without. Take heed how thou deniest to him—who, perchance, hath not the courage to grasp it for himself—the bitter, but wholesome, cup that is now presented to thy lips!’