Maybe we read different articles, because I distinctly remember reading in the article that the energy cost of CO2 capture to achieve status quo using current technology would require more energy than the world is currently producing (fact), which means the solution is unrealistic (argument).

The number one argument against this kind of doomerism is that we don't know what we don't know

If that's the number one argument, I appreciate that you don't go on to cite number two, and three, because those would have to be incredibly weak arguments.

but perhaps some technological breakthrough (genetically engineered trees? dense organic materials? who knows?) could work as soon as it is discovered.

It's also within the realm of possibilities that aliens will descend and use their superior technology to restore the CO2 levels in the atmosphere. But I would advice against a plan that could only succeed if this were to happen.