What if the 'proselytizing' was environmental instead? Switching away from meat would lessen your footprint considerably, and likely improve your health[1] even if you don't care about the moral arguments.
You can reduce your carbon footprint by orders of magnitude more by not having children, or having fewer children, but I don't see as many people advocating for voluntary sterilization (or even just abstaining from childbearing). Most people believe it's their deity-given right (and often imperative) to keep reproducing, even if our environment suffers as a result.
I point this out to suggest that at the end of the day all of this is emotional and is largely driven by how we were socialized and raised from a very young age. It's often difficult to get people to agree with rational arguments when those arguments contradict a lifetime of programming.
Having said all that, I've found that the environmental argument is the only one that gives me pause around my meat consumption.
Reducing the number of children is an aspect that rarely comes up in discussions about environmental impact (not necessarily about food), even though I find it a very compelling argument. In some countries (hint: not the US, or most of Europe), there is not even a need for much advocacy, as the concept is descriptive: fertility-rate times planetary-footprint is less than 2, so in the long run, those countries would actually be using zero resources.
By the environmental footprint argument, I could do far greater good for it by murdering the person with the largest footprint, and altering the remainder of my lifestyle not at all.
To ask those with the smallest prints to wear smaller shoes is ridiculous while some still wear a different yacht on each foot. You ask the man with the ha'penny to give a farthing, while the man on the gold throne is unmolested.
If I save the whole Earth, will I get to keep some of it, or will title to the vast majority of the habitable area remain with those who made my interventions necessary?
It's a matter of incentives. Why should I bust my ass to live green on a rented 1/8 of an acre, while my neighbor that owns the 400 sqmi ranch is buying pipes and pumps specialized to move liquefied manure by the cubic meter, and blowing cigar smoke in my face when I complain about the smell? Go annoy the asshats that can actually make a difference by changing their behavior, or save your arguments for a political campaign. My only stake in the environment is my own survival. If it down comes to that, I already know I'm expendable. I won't just lay down and die, though; I'm going to at least try to eat the rich, instead of my vegetables.
> By the environmental footprint argument, I could do far greater good for it by murdering the person with the largest footprint, and altering the remainder of my lifestyle not at all.
Sure, but you're not going to do that, so the best thing you can possibly do is alter your lifestyle and do your best to help others do the same. Pointing your finger at someone else and crying "but he's worse than I am, so why should I change?" isn't a very convincing argument for doing nothing.
> My only stake in the environment is my own survival.
Do you perhaps have children, or people that you care about that are younger than you?
We know I'm not going to go out and literally murder rich people. Not right away. I'd rather get together with a bunch of like-minded people and tax their excessive consumption. If they resist, we'd almost certainly try taking away all their favorite stuff and locking them in a people-cage before resorting to killing them.
Votes for higher tax rates on wealthier tax brackets, and for stricter environmental laws, and more enforceable penalties for breaking them, are all more effective than me, individually, setting my thermostat just one more degree towards discomfort, separating my recycling into just one more category, shortening my showers by just one more minute, and doing all that stuff we were told would make a difference.
But then one (allegedly) rich jackass screws it up for everybody, unilaterally withdrawing from international environmental agreements, and putting a fox in charge of the EPA's henhouse. It can make someone question their commitment. Why should I voluntarily endure all this eco-sterity, when I can reduce my environmental footprint to zero and still live to see the melting methane clathrates roiling arctic seas, because we were all apparently targeting the wrong people?
The people who collectively claim to own most of the planet are the ones who are destroying it. They can do as they please with their other possessions, can't they? I lost whatever direct stake I had in this planet in the wake of the 2007 mortgage crisis. I used to own land. Or I thought I did. Now I have to rent the ground on which I sleep. So if the planet is dying, I don't really have to worry about my piece of it dying. If my home is demolished by floods and tornadoes, that's more the landlord's problem: I move on to the next place. I'm just in a race with all the other doomed souls, to work hard enough to make enough money to win the bidding war to rent the last habitable place on Earth. In doing that, I may have to discard any pretense of environmental responsibility, and think solely of my own small tribe, because clearly, the cartel in place to ensure cooperation for the greater good of all civilization is not effectively checking the renegades who are choosing personal benefit over collective benefit, at a world-altering scale.
So instead of tsking at the person who threw brown glass into the clear glass bin, get violently pissed at the person who is secretively trucking those bins to the landfill, because glass recycling isn't profitable this month. Instead of frowning at the person eating a real meat hamburger, go ape on the person whose animal waste lagoon breached a levee and washed into the local watershed. I'm not going to do one more damned thing to my own lifestyle for the sake of environmentalism, as long as I think that nothing that I have already done, and nothing I am currently doing, really matters.
If becoming an eco-terrorist is the only plausible way to avoid Venus 2: Methane Boogaloo, then yeah, I think I could maybe make a difference that way. There are definitely better paths to pursue, collectively, but I think maybe the folks telling me, "Hey, you! Stop eating meat. Thanks!" while trading Bitcoin and designing the next Juicero-like company (but better this time), are not fully understanding the problems at hand, and will not be effective allies.
Thirded, even as someone who has no intent of going full vegetarian anytime soon, in the past year I've significantly reduced the amount of meat, particularly red, that I eat on a regular basis. I'm just fine with reserving my meat meals for special occasions.
1: http://time.com/4266874/vegetarian-diet-climate-change/