OK, I see. I just find this hard to defend, at least if we specify that we're talking about the same intensity of suffering. But I guess that this is the point where people declare the ratio a "terminal value" and then the discussion is over.
What I do understand is that some people think killing adult healthy humans is much worse than killing animals, because there you can conceive a clear difference in abilities that at least plausibly seems relevant to the badness of killing. But then for anti-speciesism they should also agree that killing adult healthy humans is intrinsically much worse than killing cognitively disabled people or human infants.
(Also, if killing people is so bad because it violates preferences, then that leads to a handful of counterintuitive conclusions, e.g. having to care about preferences of those already dead.)
Killing adult healthy-minded humans (who want to live) is obviously much worse than killing non-sapient human infants. But historically attempts to single out a group of humans to assign moral value to have turned out badly, so we try not to do that.
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.