> Point source capture is of course much cheaper but it cannot get us to net negative CO₂ emissions.

But it certainly can: by capturing on a point source that burns biological fuel. Without the burning, all the CO2 emitted (or captured) would have cycled back to the air a short time later anyways. And if you mainly do it to have a cheap carbon source to make some intermittent energy source you already have storable/transportable (e.g. creating aircraft fuel), just about any low grade biomass will do. Grass. Leaves. Dried algae. Paper too dirty for recycling (or rather: any paper - does paper recycling even make any sense in an economy that also burns wood for energy?). When you start looking at incineration not as disposal and/or energy source, but as a source of concentrated CO2, almost anything turns into a useful resource. All that stuff contains carbon, and it's all going back into the atmosphere one way or another.