If heretics recanted, they could not be killed. Thou shalt not kill and all that. At worst, there were put in a civil jail for life. Only if they resumed their heretical position would they be given a more severe sentence.
Most of the incidents that people use as examples of the Inquisition being "out of control" were conducted under the
name of the Inquisition, but were officially denounced by the Vatican. The Inquisition, which originally forbid the use of torture, only used torture when there had been a previous confession (which was elicited under torture by civil authorities). Very few offenses carried the death penalty. Again all of the famous death penalty cases were actually carried out against the expressed wishes of the Vatican (Joan of Arc, the Templars in France).
The horrors of the inquisition teach us:
- The uselessness of torture
- The importance of separation of church and state
- The importance of habeus corpus
- The importance of "innocent until proven guilty"
- and the importance of the right not to testify against oneself
When the Inquisition started, as I said, torture was forbidden, and there were also quite a few other things put in place in an attempt to make it fair and just. The corruption introduced by political concerns, plus the loopholes inherent in the flawed concept of "justice" made it into the historical fiasco it became.
The lesson is that we can't let "a little torture" or "a few extra-judicial cases" under passed the gate, or we'll lose justice entirely.