Edit: I'm also not trying to equate eating meat with smoking - one is obviously more harmful to society than the other. I'm just thinking about the cultural change that happened. Culture is malleable. Laws aren't a great way to affect culture, but social pressure is really effective.
The reason for the decrease in smoking is still being researched and debate, but the main arguments that I have seen is the main role of smoking as social stress relief and as such it has been replaced by other addictions like opium use (mobile phone use, social media, and games has also been argued).
If we consider food culture to be malleable, we definitely should move to aquaculture as a main source of nutrients. Farms on land compete with forests and human activity, and land based farms uses artificial fertilizers (derived from natural gas) and massive amount of fresh water. Shellfish, invertebrates, and seaweed can provide both protein and calories, and has the lowest environmental impact of anything we eat today and can even have a positive environmental impact if farmed correctly. Changing farming from doing harm to doing good would have massive impact, and all it takes is a cultural change.
It's tied to their identity for a lot of people. The same kinds that will drive a huge SUV to compensate for the hole in their lives where meaning and connection is supposed to be.
The broken US voting system amplifies the effect.
They already told us. They hate anybody who isn't a cis white christian male. There's not a lot to find consensus on when one side wants healthcare for everyone and the other wants some people to cease to exist within the country.
Veganism is an individual choice, and individual choices are generally pushed by culture
Of course culture and politics influence each other in a myriad of ways, but when people start to try and push individual choices like being vegan into the political space it is never very popular
I personally would fight tooth and nail to prevent veganism from becoming a law in my country. Failing that I would immediately make plans to move somewhere else.
That's not something most countries want
The major limiter of veganism is cultural. People love eating meat. It’s a major source of protein and calories, especially in developing countries. Americans are not going vegan, so it’s kind of silly, in my opinion, to focus on it as a solution.
Compare to building nuclear energy or solar / wind + batteries. China, the US, Europe, and India are all well-positioned to do this. The limitation is political will, which is more difficult than it should be, but definitely easier than convincing a critical mass of Americans to go vegan.