Vegans, even life long vegans, exist. We do not need meat. And the reformist position overlooks the question whether it actually works. Convincing 10 people to CONSISTENTLY AND FOREVER decrease their meat intake by 10% is the same as convincing just 1 person to go vegan (aka 100% reduction). I don't have studies either way, but anecdotally people are extremely bad at keeping up dietary/lifestyle changes, but veganism is a lot simpler. "No animal products" is simpler than "have I reached my 90% yet?".
Again, would love some studies on this, but it just seems more like wishful thinking. Additionally, we could just encourage both.
Some beliefs lead to immoral outcomes. I'm absolutely certain you can think of quite a few beliefs like that, right? Just picture a hill billy from Alabama, are all his beliefs fine?
In the end, morals is applied ethics, and politics is applied morals. We absolutely should legislate and not tolerate bad beliefs. The vague idea that "everyone has their own belief/opinion and we have to respect it" is a thought terminating cliche that makes the world a worse place. My dad wants me to respect his antivax beliefs, my grandfather wants me to respect his climate change denialism beliefs. Should I?