Individuals must only be treated as ends, never as means.

It goes "never as a mere means."

People always forget the "mere" part.

I wholly agree that beyond just sustainability, the reduction of suffering for animals is in the heart of veganism.

That being said, it's not the most effective argument to sway us meat eaters. When people think of animal suffering, it brings shame and guilt and makes some people defensive. This is why some people hate vegans, because it's a reflection of their own inadequacies. They revel at finding proselytizing vegans to pull apart because it lets them tell the world 'See? This is what all vegans are like. I'm not like that and therefore I am a good person.'

Self-interest is the easiest way to goad people into thinking about veganism without hurting any egos. If you rephrase veganism as a matter of self-preservation and not a moral issue, people are more open to that.

It's much easier to make the world eat 10% less meat than make 10% of everyone a vegan. Veganism for all isn't the answer yet, because human incentives don't work that way. Instead of promoting veganism, it's much more achievable to ask people to do things like meatless Mondays.