Liz, you over-simplified this fetish. The people with scat fetish, are only into the shit of people they adore, not just any other shit. Well I am not into this, but have a friend who is into this and many other kinks. In her words she loves to take in all the natural discharges of her lover. And she does mean ALL.
Just because this is lifestyle which we find shitty, doesn't mean we have to put down those who are into this lifestyle.