Is it disrespectful to send missionaries to evangelize non-Christian peoples, like certain indigenous tribes, when faced with the human needs of these populations?
First, it is necessary to make some distinctions so as not to cause confusion. Missionaries are missionaries inasmuch as they carry the Gospel where it is not known, in obedience to the command of Christ (Mark 16:16 and Matthew 28:19). Upon entering into contact with new people by way of evangelization, the Church is aware that not all that is found in every cultural model is positive, especially for the human person. Thus, there is work to be done prior to the proclamation of the Gospel in addressing the human needs of that culture. Nevertheless, such works of charity are themselves inspired by the values of the Gospel.
Here’s an example: there is a place where a Christian community has settled missionaries who have worked to help ensure that the people they encountered would reach a standard of living truly adequate to their human dignity. The fight against poverty, the critique of social systems (such as castes in India), the condemnation of polygamy and of slavery are all aspects of this effort on the part of Christians to correspond to the human needs of the society, and is independent of whether or not some of those people then become Christians.
Thus, it is not really a lack of respect for these populations to introduce and inculcate into their culture stimuli that are capable of inspiring a new way of acting; it is only the first phase of a Christian action of leavening, in which one finds the proclamation of the Gospel as the culmination of a journey. Certainly, the critique of particular social models (specifically, of certain practices within non-Christian cultures) can lead to tension, but these are beneficial tensions. Though in the past, efforts to evangelize may not have been carried out in the best possible manner, these experiences are part of the history of a maturing process of the missionary method, whose ultimate goal is the salvation of souls for the glory of God and for love of mankind.