As with all reactionary positions among allies or comrades, we must envision how to build a world in which they are abolished through practice and consciousness.

This is not just because we have duties as socialists or whatever, but because it's the only way we can, as individuals, practically organize without developing misanthropy. You won't just find carnist socialists out there repeating absurd reactionary talking points and reverting to bullying behavior to punch right on this. It's also not the only time you'll find people, including socialists, draping themselves in an identity in order to deflect from a criticism. Socialists, particularly Western leftists, are also pissbabies that fall apart during basic disagreements, though luckily more and more are developing the skill of patience and seeking understanding.

So, to move past it, you have to focus less on the reactionary they are (on a given topic) and instead on their capacity to eventually change or to indirectly help us build by putting more people into the pipeline.

For a non-vegan example, there are many racist socialists out there, having absorbed the base level casual racism of their societies as well as any personal peculiarities. You actually can't operate as a socialist in the West without contending with this. If you made your org truly antiracist in the sense that you purged everyone holding onto any casually racist views, you'd no longer have organizations at all. There is casual racism in black socialist groups, in indigenous groups, in South Asian groups. Much of it internalized. If we couldn't handle that racism and try to correct it, we would have no organizations at all.

I would recommend getting vegan comrades so that you can have a safe place to retreat. When you run out of steam fighting with reactionary sentiment, they can be a way to recharge. They will also be how you win people over. One person saying veganism is good is just a person with the right opinion. A small group is an organization that can recruit and influence.