Why does Danforth refuse to postpone any further hangings?
The state of Salem is very bad. Reverend Parris fears rebellion as they've heard occurred in Andover, nearby. Cows and orphans wander the highroad while crops rot, unharvested in the field. Parris has received what seems like a death threat: a dagger stuck into his door. Very few people came to witness Proctor's excommunication from the church, and this betrays the community's disagreement with his conviction. All of this is used as evidence to convince Danforth that the hangings scheduled for today must be postponed. However, he says:
Postponement now speaks a floundering on my part; reprieve or pardon must cast doubt upon the guilt of them that died till now. While I speak God's law, I will not crack its voice with whimpering. If retaliation is your fear, know this—I should hang ten thousand that dared to rise against the law, and an ocean of salt tears could not melt the resolution of the statutes.
Danforth fears—first—that he would lose credibility and authority if he postpones the hangings. If he pardons or delays the execution of those scheduled to die today, it will cause people to question both his authority as well as the guilt of the others who've already been executed for the same crimes. He reminds everyone that the law is from God, and that he is the arbiter of that law. He promises that, if there is a rebellion, he would likewise punish rebels with death. In other words, then, Danforth would rather hang thousands in order to maintain his power rather than save the lives of innocents and risk losing that power. Retaining his authority, not seeking truth or even upholding the law, is his top priority; he will not postpone the hangings.
Already, there have been twelve hangings with another seven scheduled to take place. Though having found that Abigail has run off with her uncle's (Reverend Parris) money, thus making it clear that she was in fact guilty of lying about being bewitched and about her accusations against others in town, Danforth knows that turning back on their initial stance against believed and, according to him during the trials, "proven" cases of witchcraft would result in nothing more than loss of credibility on their part before the opinions of the town. Postponing any further hangings would be like giving in and admitting their error. At this point, though, with so many who have already died, the families of the hanging victims would come down upon the courts with such hatred that complete anarchy could ensure, forcing Danforth and the other officials into very compromising situations. Parris makes this concern clear to Danforth when he states, "I fear there will be riot here" (Act IV).