When Danforth says this line, he is essentially showing that he is taking a very hard line against the people who have been accused of witchcraft. He is basically saying that all the people who have been accused are guilty and are evil and corrupt (sinful).
At this point in the play, many of the people (including Rev. Hale) have grave doubts about the trials. They feel that the trials are starting to convict innocent people. This has come about because well respected people like John Proctor and Rebecca Nurse are going to be hanged.
But Danforth will admit no doubts. He is going to stand firm and maintain that all who are accused are evil people.