I live in a tiny rural town, and get the majority of my meat from farmer's markets. Having been raised on a similar farm to the ones I buy from, I'm willing to bet those cows are happy a greater percentage of their lives than I will be. I recognize this is mostly working because of where I live and the confidence I have in how those farms are run. In the same way that encouraging fewer animals to exist in terrible conditions (by being vegan) is good I feel that encouraging more animals to exist in excellent conditions (by eating meat) is good. I don't stop eating meat (though I do eat less) when I go on trips elsewhere even though I'm aware I'm probably eating something that had a decidedly suboptimal life because switching on and off veganism would be slow.

That's my primary argument. My secondary, less confident position is that since I prefer existing in pain and misery to not existing, my default assumption should be that animals prefer existing in pain and misery to not existing. I'm much less confident here, since I'm both clearly committing the typical mind fallacy and have always had some good things in my life no matter how awful most things were. Still, when I imagine being in their position, I find myself preferring to exist and live rather than not have existed. (Though I prefer existing and not being in pain the superior outcome by a wide margin!)