That is completely ridiculous as it is irrelevant here.
The Mormons in question have lived in this part of Mexico for a hundred years. Missionary trips they may take to other places are unrelated to what just happened to them here because they were at home.
These weren’t Americans traveling in Mexico.
These are Mexican Mormons who had anchor baby children.
Sorry but these people whether they called themselves Mexicans, Mexican Americans, World Citizens or whatever were a distinct alien group within an established endemic culture. They looked, acted and behaved differently than the native population. When this phenomena occurs anywhere, regardless of the religious, social or political motivation of the newcomers, there is more often than not eventual barbaric violence and massacres. Read history. There is also a large Hasidic settlement in Mexico. They too are in danger.
BTW do Mormons send their young people as missionaries into Muslim countries? One would hope not.
They had mexican american citizenship and are fundamentalist
LDS seems like odd background as the story unfolds.