I smell a variation of Pascal's Mugging here. In Pascal's Mugging, you are told that you should consider a possibility with a small probability because the large consequence makes up for the fact that the probability is small. Here you are suggesting that someone may not be "very sure" (i.e. that he may have a small degree of uncertainty), but that even a small degree of uncertainty justifies becoming a vegetarian because something about the consequence of being wrong (presumably, multiplying by the high badness, though you don't explicitly say so) makes up for the fact that the degree of uncertainty is small.