"Why are so many so enamored by this unpleasant experience of swallowing unusual liquids and examining their fecal output?"
Perhaps people have had digestive problems. Which were improved by doing liver flushes. Did you ever think of that?
Did you ever think that maybe the condition of ones fecal matter might gain some insight into what may be causing the digestion distress? Do you think trying to humiliate people through your verbage is going to cause them to conform to your False Evidence Appearing Real?
"Is it a strange form of anal fixation?"
Have you ever had digestive discomfort for years, and then been put at ease from simply ingesting a cup of olive oil?