Any land reclaimed from livestock feeding could be returned to nature, be it rainforests in Brazil or woodlands in Europe. Livestock uses a massive amount of agricultural land in comparison to plant production meant for direct human consumption.
It's just a very very simple math based on the amount of crops it takes to grow animals for meat -- and soy is much more efficient than grass in that sense, so your suggestion would make things decidedly worse for environment.
It's just a very very simple math based on the amount of crops it takes to grow animals for meat -- and soy is much more efficient than grass in that sense, so your suggestion would make things decidedly worse for environment.