Meat animal farming contributes to climate change and abstaining makes the demand for meat lower. It’s actually perfectly consistent.

abstaining makes the demand for meat lower.

no, it doesn’t.

Demand just means how much is bought. Less bought is less demand.
I’m pretty sure more is bought every year, not less

Less than it would be with X people plus 1 (me)

Are you deliberately being obtuse?

if you buy something, it’s not available for someone else to buy it.

also, you can’t prove a counterfactual.