My wife's ancestors came over on the Mayflower and has done extensive genealogical investigation and on the witch executions in Mass. She is convinced that many of these executions were carried out for political reasons where women received inheritances and others wanted it. One of her relatives with wealth was executed as a witch. We should never underestimate the evil and power of politics and the willingness of those without ethics and with ambition to do whatever it takes to advance their own interests. I agree if one is actually caught in the act of a crime then kill them outright, otherwise capital punishment needs to be applied only if the crime is nailed down 100% by facts, not just witnesses.
Not a single conviction after that point.
If there had actually been a conspiracy, a point of evidentiary law wouldn't have stopped it. Rev. Mather was a pompous ass, but he was an honest man.
Another problem is that these people actually believed in witches, something we find hard to fathom. As C.S. Lewis noted, if we still believed that people could sell their souls to the devil in exchange for the power to make their neighbors sick and kill them and their livestock, "if anybody deserved death, then these filthy quislings would."