Plowing pasture-land to grow soybeans is likely to reduce bio-diversity even more than running cattle on that land. A lot of pasture land is marginal land w

Plowing pasture-land to grow soybeans is likely to reduce bio-diversity even more than running cattle on that land. A lot of pasture land is marginal land where a plow is very destructive, and is often a lot closer to the pre-human ecology where the land was grazed by large mammals. Your primary point still stands -- eating tofu likely has a lower ecological impact than eating beef, but the trade-off isn't obvious, and second order effects can be significant. If you stop grazing cattle on land, the owner of that land is going to find another use for the land to profit from it. Some of those uses are going to be better for bio-diversity, some are going to be worse. It's highly unlikely to become parkland. So will going vegan reduce greenhouse gas emissions and increase bio-diversity? Probably, but not certainly. This uncertainty shouldn't dissuade people from acting on "probably" though.