This is like when people argue that death penalty is bad because it's so expensive. Then it would follow that their argument becomes disarmed if we make the death penalty cheaper. Somehow it feels like they were really arguing that death penalty is evil, but they came up with a logistical argument. Logistical arguments have logistical solutions. This is a consequence of working backward from a feeling they wanted to justify -- the problem framing and solution are orthogonal to what they really want.
If we were to talk about climate change or ecological damage, our focus should really be on energy and pollution from industrial and transportation output.
I also think my point stands that I haven't heard of any clear and convincing moral or ethical framework for veganism. You're building a sideways case for climate change.