I'm Argentinean, if I stopped eating meat my passport would probably be revoked. I grew up thinking that it was perfectly normal to eat meat 7 days a week. Even with this background, I started reducing the amount of meat some time back. I'm not vegetarian by any means, but I reduced my meat consumption about 80% without even trying. I'm sure there are lots of people that could too.

> Less humans due birth control or fortuitous events (e.g. a plague)

Like everything, consumption follows a Pareto distribution, where some "whales" drive most of the demand. You can focus on them instead of hoping for lots of people dying.

Also, reduce poverty and the amount of newborns in this planet will naturally decrease precipitously, without any need for a mandate from anyone.