Maybe it's time for some serious testing. We could lock all the Breatharians in a well ventilated room for 40 days without food or water.
The homeopaths could be in the next room with just a supply of really nice water. Those who claim prayer is the answer to everything could be just left in their room since their god will unlock their door when they are ready to leave.
Seriously (ok I was a bit serious there) I think one reason they are not sectioned is organised religion. The churches added (demanded/forced) an air of respectability to irrational babbling. Also we couldn't go around putting breatharians in padded rooms without making space for Bishops and such.
Imagine the assessments!
"You believe that if you breathe deeply you don't need to eat or drink."
"Go with the attendants and they'll find you a nice room"
"So to recap. You get together with friends and eat the remains of your founder. This is conjured up by saying the right magic words. If you do something immoral you get someone to say some more magic words to make it right"
"Go with the attendants and they'll find you a nice room"
"You voted Tory?"
"Go with the attendants and they'll find you a nice room"
Okay, maybe the last one is borderline :)