I agree with you in terms of priorities, and in a concern that small gestures might be one step removed from "slacktivism". ("I don't have to call my congresscritter; I don't eat meat!") For that matter, I think the law of unintended consequences should be brought into play. Let's be honest - cows would be near extinct if we didn't farm them. And the farm land that currently raises meat, in my estimation, would likely become big box stores or McMansion developments (or as you say, industrial commodity farming), not forest or prairie.
Still, I feel the need to be careful in comparing or ranking ethical behaviors. I believe hardly anyone does all they can. Our greatest environmentalists log thousands of dirty airline miles spreading their message; they spread their message on dirty paper and dirty electronics. On balance, they believe they're doing what they can, and hopefully they engage in the self-reflection to do a little more when they can. I hope vegans and vegetarians do the same (and my experience is that many do).
I've felt the militancy among vegans and vegetarians which I think you're referencing, and I worry that it's off-putting and damaging to the coalitions we need to preserve the earth's climate as we like it. But I think it's the holier-than-thou attitude which has to go, not the dietary choice.