I agree that one has to adjust for certainty and overconfidence, and peer disagreement does seem like a good reason to downshift as well.

OK, I see your point about shooting, agreed.

Regarding popularity, if that's the only criterion then also fAI would be a pet cause. I'd say it also depends on popularity among which group of people. Out of the smartest and most rational people I know, the majority of those who are interested in doing ethics, ie. in figuring out what "being altruistic" implies, would agree that animal suffering counts just as much as human suffering. And the smart and rational people who disagree are mostly not interested in doing ethics (in this way), as they just claim that it is all about "what they care about", a selfish defense that could just as well be used to uphold racism or sexism.

So on the above grounds I'd object to vegetarianism being a pet cause.