Somehow, vegan-inclined folks never seem to factor in the mass-genocide of domestic breeds that is necessary to achieve their particular utopia. We're talking 1.5 billion pets, 5 billion livestock, and 28 billion poultry - none of which are remotely able to survive on their own in the wild.
You are aware that all of these livestock animals didn't exist a few months to years ago? And that we go through these animals every couple months-years?
Everyone going vegan would just mean we'd stop repleneshing them.
Keep in mind that we already have to perform widespread culling of wild animals in this category. Having eliminated most of the apex predators, we're on the hook to keep populations of wild horses/cattle/deer/etc in check.
If we cease to use domestic animals, they end up in the same boat - we're no longer paying to feed and house them, and if they are capable of breeding in the wild, they will breed unchecked. Leading us to cull them, ad infinitum
The "genocide" that you describe is happening constantly. None of the chicken we have today will be alive in a couple months. We kill them to eat them.
If we cease to "use" them, we just keep that "genocide" going for a year, but we just stop breeding new ones. The result is no more animals after a few months/years. And you didn't kill any more than you would have anyways.
If you have a sink that is half full because the inflowing water and the outflowing water are in quilibrium, you drain it by turning off the tap (breeding).
"Carry on for a year and then it's all good" is not one of the available choices.
Your choices are (a) wipe out the species entirely, or (b) allow them to continue breeding on their own, and commit to culling them for the rest of eternity.