The Salem witch trials (1692) are important today for a couple of reasons.
First, the trials occurred because there was no separation of church and state. Witches were the supposed servants of Satan. Persecution of witches was a type of religious persecution. Persons who seemed odd or who did not worship fervently enough were sometimes accused of witchcraft. In colonial New England, the same people typically led both the church and the state. Today, church and state are separated in the United States and most other advanced nations.
Another reason why the trials were a miscarriage of justice was the lack of modern-day legal safeguards. Today in America, the accused are entitled to legal representation. At Salem, the accused witches were not defended by lawyers. Also, dubious "spectral evidence" was allowed in the court at Salem. Further, the accused witches were presumed to be guilty and were not permitted to cross-examine their accusers.
In summary, witch trials are not possible in secular nations with modern systems of jurisprudence. They serve as a warning of what can happen when these safeguards are not in place.