Well obviously hundreds of people going vegan isn’t going to make much of a difference, because we have billions of people.

That doesn’t mean an individual vegan can’t make a difference by spreading their lifestyle.

It’s just like any moral improvement: an individual should not expect that their individual actions are going to change the world.

Also yes, there’s no 1-to-1 correspondence between more vegans in a particular neighborhood, and cows not being born and then slaughtered. It’s understood that these two pools are too far abstracted for tracing farm animals to meat eaters.

But the same problem is true of voting too. So if a vegan shouldn’t expect to make a difference by converting others to veganism, then a citizen shouldn’t expect to make a difference by voting either.