Machiavellian missionaries

I have had recently the opportunity to chat with a missionary who has been working as a bush doctor in Western Africa. I find it quite admirable that a Westerner is willing to leave easy life aside and spend many years in the middle of an inhospitable nowhere to help others. Of course, the end goal is to spread Christianity, and I have no problem if these free health services are provided through a sponsor.

What I found very disturbing, though, was the approach to converting the locals. Indeed, missionaries tell these pagans that now that they know about God, Jesus and the Bible, they will go to Hell if they do not convert. They would have avoided that fate had they remained ignorant. The missionaries are devout Christians and believe this as well. Can we then really say they care about the locals? They willingly paint the pagans into a corner, threatening them out of nowhere with the worst possible outcome in their afterlife. What is then the point of making terrestrial life a little better? In the end, many locals would much worse off after the arrival of the missionaries.