Yes I understand this must be infuriating. Have you tried complaining to administration - maybe the administration don't realize how their presence is stressing some students.

Where I live we occasionaly get a certain door to door religious group and when I was a kid they would often canvas our neighborhood. I really dislike them immensely - how would they like it, if someone came and pushed another religion on them. I have my own religion and it's an insult to me to preach their ideas on me. Once when my mother told them she wasn't interested and tried to close the door - the guy put his foot between, so she couldn't close it. They're religious bullies.