The claim here is that going vegan won't change anything because not enough people will go vegan, and that one person won't make a difference.
Carnists also claim that you shouldn't go around trying to convince too many people. So which is it? Should you be a pushy vegan trying to convince people to join or should you not? Both these arguments are just filibustering with bad arguments.
Every small increment of demand is one less tortured animal. If you purchase an animal product, it echoes up the supply chain and results in animals needlessly dying. If there is one less bag of frozen chicken bought, then the order of a box of frozen chicken bags is pushed back by one bag. Then the production line is shut down one box earlier. Then one box's worth of chickens doesn't get trucked to the facility.
Every single person going vegan absolutely makes a difference. Every vegan normalizes the position that needlessly torturing animals for your entertainment is wrong, and every carnist is giving other carnists around them tacit approval.
This isn't an all-or-nothing game, every percent of people going vegan makes an incremental difference in third-world hunger. If 1% more people go vegan, that is just that much less damage done to other people.
This is just another argument from moral nihilism