That's actually not true. We do have food scarcity. Just not yet in most of the world. You see, our current food production models, especially meat production but also plant food production, are highly unsustainable. It is very likely we will enter into a global famine that wipes out most of the human population sometime in the next couple centuries. It could be much sooner, could be near the end of that, but it will happen if we continue as we are now. That is because the way we farm currently uses far too much non-renewable water sources (aquifers for example), fertilizer that comes from non renewable sources (derived from fossil fuels), and land that is having its soil drained of nutrients. Veganism alone does not fix these problems. It can make them easier to solve in many cases because we waste less resources on cattle, but cattle is also only so wasteful because of HOW we use it. Back in medieval times cattle was a way to turn useless land (grazing land not suitable for crops) into calories. They'd have a small herd and let it free range. This was a boon of calories not a drain. And meat was rare to consume as a living cow makes milk and is much more valuable than a dead cow. Same with chickens and eggs. Even pigs produced useful manure for fertilizing. So while they did slaughter and eat them it wasn't the sole purpose of raising those animals. And the animals made their lives possible through their byproducts.

I would say that the goal of any vegan should be to find a way for us to live in harmony with animals and the environment. Because we aren't just talking about farm animals, and humans don't just harm animals for food. Our farming practices destroy their natural habitats as well. Even if we ate only plants if we do not find a more sustainable way to farm animals will continue to suffer.