The justification for these things is that the oxygen is being converted to CO2 faster than CO2 is being reduced back to oxygen. So if you capture CO2 at a high rate eventually this would lead to you capturing all of the oxygen.
We’ll run out of CO2 through the natural version of this process (weathering) long before the O2 encounters this problem. At that point all the plants die, still with plenty of O2 in the air.
In other words, it’s the carbon content that’s more endangered over the next billion years than the oxygen.
The problem with this technology isn’t side effects like this, it’s prohibitive power requirements.
