Despite Miller stating that he did not purposefully create a parallel between the McCarthy trials and the Salem Witch trials, it similarities are undeniable. Both trials were the result of an abstract fear that turned into hysteria. In the Salem Witch Trials, the fear was that Satan was loose in the village. In the 50's, the fear was the communism would overtake America. In both situations, people were accused without concrete evidence. In both situations, people were gulity until prove innocent, rather than innocent until proven guilty. Finally, both situation were escalated by fear and the "mob mentality" that overtook their respective societies.
There are some differences in the historical events as well. The Salem Witch trials were based on supernatural testimony. They are also theorized to have been caused be a power struggle within the community. In Salem, if you confessed you were released, if you denied you were hanged. During the McCarthy trials, the sequences were not as deadly. People were black-listed, even if there was no hard evidence. The basis of the evidence was circumstantial, but not supernatural.
Overall, the similarities outweigh the differences.