If people aren't buying factory farmed animal products, the agricultural industry wouldn't still be using awful practices. The supply and demand chain is complicated and the agricultural industry can choose different levers than lowering production, but those different levers would result in lower profit either for example by higher advertisement spending or lowering prices. Over time with a sustained vegan effect, the market would correct itself, since companies hate losing money and will pursue more profitable alternatives, and fewer animals would be slaughtered.

Your own wallet is a very large vote. But voting in elections or advocating for change in other ways are of course also very important. They shouldn't exclude each other.

People are allowed to do with their body as it pleases, as long as they don't hurt anyone. There are quite a few scenarios, where I don't think you would agree with your own statement.