What I mean is that scrubbing the CO2 leaves you in a scenario where the air is just as dangerous as before (no oxygen) but you don't have any reflexes or senses letting you know of the danger.
It’s the co2 in your blood that you make in your body( not that you breathe in) that makes you want to breathe. You can breathe pure oxygen and you will still feel the need to breathe, because your body uses the oxygen to make co2 which then needs to be expelled.
That only applies (gives you a trigger that you should breathe when the environment is dangerous) if you never exhale though. Is that really an argument for the technique being safe?
What if that's not the case though. Spaces that are high in CO2 are dangerous because the CO2 has displaced the oxygen below a safe percentage. Maybe by scrubbing the CO2 we can increase the oxygen concentration.