The point is that given the way these probabilities add up, not only wouldn't that work for a single bacon omelette, it wouldn't work for a lifetime of bacon omelettes. They're either all harmful or all non-harmful.

I know. Are you implying that we shouldn't maximise expected utility when we're faced with lots of events with dependent probabilities? This seems like an unusual stance.

Your reasoning doesn't depend on the exact number 20... If the probability was 1% or 0.01% you could say exactly the same thing and it would be just as valid.

My reasoning doesn't depend on the exact number 20, but the probability can't be arbitrarily low either. If the probability of cow sentience were only 1/1,000,000,000,000, then the expected utility of being veg*n would be lower than that of eating meat, since you would have to learn new recipes and worry about nutrition, and that would be costly enough to outweigh the very small chance of a very bad outcome.

In other words, your reasoning proves too much; it would imply accepting Pascal's Mugging. And I don't accept Pascal's Mugging.

Again, this depends on what you mean by Pascal's Mugging. If you mean the original version, then my reasoning does not necessarily imply being mugged, since the mugger can name arbitrarily high numbers of people that they might torture, whereas you can figure out exactly how many non-human animals suffer and die as a result of your dietary choices (if you're an average American, approximately 200, only 30 if you don't eat seafood, and only 1.4 if you also don't eat chicken or eggs, according to this document), and nobody can boost this number in response to you claiming that you have a really small probability of them being sentient.

However, if by Pascal's Mugging you mean "maximising expected utility when the probability of success is small but bounded from below and you have different sources of uncertainty", then yes, you should accept Pascal's Mugging, and I have never seen a convincing argument that you shouldn't. Also, please don't call that Pascal's Mugging, since it is importantly different from its namesake.