I notice that a large fraction of Effective Altruism people are vegetarian. This makes sense: in general Effective Altruists take moral issues seriously, even when that means changing your lifestyle. I'm not sure it's a good balance, though.
One way to think about this is to convert it into money. How much would I need to be paid to give up eating meat? All animal products? How much money would I need to spend on myself to be about as happy as I would be with less money but continuing to eat animals? I'd probably be willing to go vegetarian for about $500/year, vegan for maybe $2000/year.
It turns out you can probably pay to convince other people to be vegetarian much more cheaply than that. I estimate the cost of a vegetarian-year at $4.29 to $536 while Brian Tomasik estimates $11 with better methodology (which I looked at). This is by placing ads on facebook for a site where people can watch an animial cruelty video and ideally become vegetarian or vegan.
If you would get more than $11/year worth of enjoyment out of continuing to eat meat, why not give $11/year to convince someone else to not eat meat for you? Or give $50/year and be on the safe side?
(While you're giving money, you should probably give it to the organization that you think will do the most good with it, which I think is probably one of GiveWell's top charities. The nice thing about money as opposed to actions is that it's easy to redirect.)
I also posted this on my blog.
As it turns out, I actually do think eating animals is approximately 1/1000th as bad as killing people.
I don't go around shooting people, a) it's a clear net loss to create a world where people kill for all their pet causes, b) it's pretty obvious that when you're trying to change a policy affecting the entire world, killing people will almost only hurt your cause.
"Don't kill people" is a pretty obvious moral schelling point that everyone can agree on.
It's dramatically less clear where lines are drawn with regards to emotional manipulation. The entire human experience is basically based around emotional manipulation (storytelling, fashion, advertisements, literature, tribal excitement at sporting events). Refraining from doing that won't cause the rest of humanity to stop, unless you're actively coordinating with people on a campaign to stop emotional manipulation.
So I'm not sure why I'd refrain from doing that, whatever my pet cause, unless my pet cause was removing emotional manipulation from humanity completely.
So is "don't inflict suffering". At least some part of what people consider bad about killing is that it can be painful or that it causes sadness in others.
I find it interesting that when it comes to eating animals, people usually focus on killing, even though most veg*ans I know care primarily about preventing suffering.