On the topic of missionaries, I have pretty strong and inconsistent opinions.
I do not approve of people trying to convince others that they should give up their own religion (or language, clothing, family structure, food preferences, etc.) in favor of some belief from another culture. I especially don't like it if the new religion is being introduced by a wealthy, powerful country with political influence over the foreign government. This is colonialism, pure and simple, and is as evil as it gets
The people involved in the mission activity don't see it this way, of course, and only think they are helping the poor down trodden. They are just bringing food and medicine, building a school, or opening a community center. Or leading a youth camp.
But they are still part of a neo-colonial enterprise. The local people usually have no say in the matter, often because they really do need the help, and have to accept the religion along with it.
They are almost as harmful as the missionaries who fought to convert the souls of people in the Americas centuries ago. I say almost, because at least they don't infect the locals with smallpox or measles and wipe out 90% of them.
Now having said all that, I want to add that I have worked with foreign missionaries in Africa and Latin America. Usually, the local people are Catholics and are being missioned at by various sects of Protestants. The Catholics don't have to mission-- they are pretty entrenched in most third world countries already. I have hung out with missionaries because they bring news from the outside world, along with Cheez Whiz and other foreign delicacies. They usually have plenty of money to spend.
And I try to explain, gently as I can, that they can help people without trying to make them change their faith. Also, I have informed them of the past colonialism that resulted in the people having the faith they now do. I have found many of them to be very receptive, because the people who go on missions are often the more adventurous-minded folks of their churches.