Earlier quoted context omitted.
There still must be some input of energy. From what I understand, the Sabatier reaction is really only viable from an environmental perspective if it is powered by some other non-carbon energy, such as solar or wind.
And if you have that surplus clean energy, you should spend it powering things that would otherwise be powered with fossil fuels - not trying to offset someone else's emissions. Carbon removal only makes sense in a world where nobody is burning any fossil fuels, and we're trying to lower atmospheric carbon. Lower, not offset.
I accept the argument that offset schemes have difficult practical problems, but at least theoretically “offset” means “lower”. It just means that your application isn’t necessarily reducing carbon. And it kind of makes sense—for an airline to get carbon neutral it would require immense investment in electric flight and decades of research and then more decades of incremental rollout. Instead that money and effort could be spent helping reduce a lot more carbon elsewhere now (e.g., replacing coal power plants with equivalent solar power).