Using foodstock, or land that even competes with foodstock, or land that is important for sensitive ecosystems or CO2 balance is obviously all out of the question if this technology is to be viable.

It's possible to make sustainable jet fuel using trees from forests that aren't competing with food supply. Without that, yes, it's a bad idea. Anything involving soy or palm is usually also a bad sign. But in principle, nothing says you can't use "good" raw materials to produce fuel.