Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic takes aim at the Golden Rule -- "Do unto others as you would have them do unto you" -- by exposing a logical edge case. Jesus delivers the famous ethical teaching, and a man responds that he has "a fetish for being surprised at night by men dressed as anatomically correct porpoises." Jesus starts to object, saying "Well, there are limits to--" but the man cheerfully says "Seeya later!" and runs off, presumably to go inflict his fetish on unsuspecting others. The caption reads: "There is no such thing as a perfect ethical law."

The humor lies in the reductio ad absurdum of the Golden Rule. While the principle is meant to encourage empathy -- treat people the way you'd want to be treated -- it implicitly assumes that everyone's preferences are roughly similar. If someone has extremely unusual desires, following the Golden Rule literally would lead them to impose those desires on others who do not share them. This is a real critique in moral philosophy: preference-based ethical rules struggle with edge cases where individual tastes diverge wildly from the norm. Weiner uses an absurdly specific fetish to make the philosophical point in the most ridiculous way possible.