The recent killing of an American missionary who tried to contact an isolated tribe on a remote Indian island has revived a debate within the evangelical movement over the extreme lengths that some missionaries are willing to go to in hopes of spreading their faith.

In the time leading up to his fatal mission last month, John Allen Chau was surrounded by like-minded people who believed he was on a divine mission, called by God to minister to uncontacted people. The group that trained Mr. Chau for his mission and others have defended his actions and even hailed him as a martyr.

But other evangelicals argue that his push to contact the tribe on North Sentinel island, a group protected by Indian law, was reckless and unjustifiable. Some religious scholars, including evangelicals, are uncomfortable with Mr. Chau’s approach. Scott Moreau, a professor at Wheaton College Graduate School in Illinois, is one of them.

“I’m appalled by the naïveté of thinking you go on a beach, you throw a fish at some people, you holler at them, and then you come back and spend the night and everything is going to be fine,” Mr. Moreau said. “It doesn’t show much sensitivity, and it doesn’t show much common sense.”