This only makes sense when operating under the assumption that "space not directly used by humans is waste". The hope with plant-based meat and cultured meat is that the surplus land just goes back to nature.
So much wrong here I don't know where to start..
This user fails to realise non-human animals require water, they produce methane, and all the machinery required to slaughter and transport run on fuel and electricity which also produces GHG.
Vegan misinformation = scientific consensus apparently
In terms of land use, the "marginal lands" idea means:
This also assumes the only things worth growing are crops that are easily harvested by mechanized means.
You can grow plenty of food on a steep hill side, you just have to terrace it and can't use a tractor.