Because some people get food aggressive, and even a mention of a sustainable diet that doesn't depend on cruel treatment of animals get them all riled up
This might just be me, but an exclamation point ruins this joke, and many similar ones
With no exclamation point, I read this as a very dry, very serious response, and the comedy comes from the absurdity of what's said with a straight face
When I see the exclamation mark, my brain goes "BOOMER BOOMER BOOMER"
Eh, as a native English speaker, I thought it was good. I have pretty low standards though, and I like other corny jokes like saying you're vegetarian because you only eat other vegetarians (e.g. cows).
It's true that animal agriculture has a huge impact on the environment compared to feeding crops directly to humans.
so get out of here with that nonsense that veganism is religious zealotry. I don't have time to cite a source for each point, but they're all super easily verified. Veganism is looking at the impact of your choices with clear eyes and choosing compassion over personal pleasure. It's choosing to live and let live, rather than forcing death and misery on other species because you like the taste of their flesh and secretions.
Anti-vegans are way more annoying and overzealous in my experience. I rarely see the stereotypical asshole vegan but I do often see the obnoxious anti-vegan.