Are grains vegetables?
How would you like to define vegetables?
And do note the very first line in my last post. I’m the last person to dismiss the distinctions between culinary and scientific food definitions. I’m only pointing out the unlikelihood that people hear “vegetarians replace meat with vegetables” and think vegetarians are limited to a very strict definition of the term.
While full vegans and vegetarians make up less than 10% of the population, the number of Democrats who are making an effort to eat less meat is much higher. In fact, I bet the percentage of ‘well-meaning liberals’ who are eating less meat is even higher since not all Democrats are liberals. Since beef is the most environmentally-damaging meat, I bet liberals eat even less beef than other meats like fish. So, I think the OP is a bit of a strawman.
Also, one of the links in the OP suggests that the meat industry produces more greenhouse gases than all transportation. Every statistic I’ve seen shows that transportation produces about 27% of the greenhouse gases while the agriculture industry produces less than half as much. I’m probably missing something, but I don’t know what.
Well this is why “plant based diet” is becoming more popular. Vegetarian itself is a poor name, as per the USDA someone who only ate vegetables wouldn’t eat bread. I can only say that when people hear I’m a vegetarian a lot of them ask me if I eat a lot of salads. Meatless diets are so… unusual, still, that it’s like people can’t grok what it would actually look like to replace the meat in their diets. I feel like people think we replace meat with salads, or meat with broccoli.
Because the vast majority of omnivores have zero need to understand the protein components of non-meat dishes. Somebody who has that much trouble grokking meat replacement probably has little to no understanding of the nutritional importance of protein beyond a vague idea that a complete meal includes meat. Hell, I’ve known a neophyte vegetarian or two who didn’t have that understanding and got ill as a result. “Make sure to replace meat with other high-protein stuff” is not common sense. It’s learned knowledge.
I think it has less to do with the term (though vegetarians are of course absolutely free to call themselves whatever they want) and more to do with a complete unconscious ignorance. I never learned about it until a period where I was cooking lots of big meals for a group that included several vegetarians and needed to educate myself.
I read that graph completely differently than you do. Except for the last two or three years, there has been a steady decrease in beef consumption. The environmental impacts (greenhouse gas production, land use, water use) of eating beef and mutton is several times larger than chicken and pork. So everyone becoming flexitarian would make a big difference.
I’m sure they have beans and rice at the grocery stores even in small towns and rural areas. But let’s start with the big cities. Let’s get 100% of the people in the big cities to go meatless, and then work our way out from there. But in these small towns and rural areas people can have backyard chickens and eggs. I think that’s sustainable.
IIRC, ketchup is a vegetable.
We should start with a $100/lb tax on meat and meat products. That will cut consumption.
Then eat peanut butter. It’s the food of the gods. What more can I say.
Or create a black market.
Or hummus. Hummus with tahini is a perfect food - you can live off it exclusively.
Hummus is OK, but flavor-wise. it comes up short in the divine food department. OTOH, I could eat two-three pounds of PB per week. In fact, I do.
Or cross-border international smuggling.
Why are you guys arguing over semantics? Legumes, cereals, fruits, berries or whatever - plant kingdom. Meat - animal kingdom. The discussion is “eat less meat, save the planet” not “I ain’t gonna replace my steak with brussels sprouts”
Change two letters in “semantics”, and you get “pedantics”, and SDMB is frequently host to copious pedantry. 
Yeah, that’s a better name. In culinary terms, “vegetarian” suggests eating culinary vegetables, not food that is made of vegetable matter in a botanical sense.
And yes, the needs of vegetarians are not well understood. All my vegetarian friends complain that if they go to a restaurant and ask for vegetarian options they are offered the salad without the chicken on top, or pasta without the sauce, or… And it’s unusual for a restaurant to offer to replace the meat with anything that has protein, or even calories.
I suspect their options have improved very significantly over the last three decades. It might not be perfect but it has improved immensely. I doubt decent alternatives are that unusual, but certainly some restaurants are better than others at non-meat products.
Some have said that ketchup and highly processed fries were called “vegetables” to allow school and hospital cafeterias to meet guidelines without actually offering more nutritional choices to patrons. Not for botanical reasons. While probably true, I suspect most deem potatoes to be plants. Ketchup, less so.
Sooooooo, ketchup is meat?