The point is that in the scenarios you described CO2 increases at the cost of oxygen, which is obviously not good, and that's what GP was referring to as "everything else is fine". It would be interesting to see what happens if instead some of the nitrogen in the air is replaced by CO2. But that's obviously not what usually happens. And there are far more damaging air contents to worry about. Like mold spores.

A crucial difference to CO is that CO2 doesn't cause permanent damage as long as oxygen supply is restored in time. Compared to that, hemoglobine touched by CO becomes essentially useless for the body since CO has a similarly high binding affinity to hemoglobin as oxygen. Recovering from that pretty much requires replacing the affected red blood cells.

> It would be interesting to see what happens if instead some of the nitrogen in the air is replaced by [CO₂].

Well, if you think it would be interesting, click the NIOSH link I provided and read the references, because that's pretty much what they're talking about.

> A crucial difference to CO is that [CO₂] doesn't cause permanent damage as long as oxygen supply is restored in time.

This is not correct; CO₂ poisoning can cause permanent injuries, including death, even when oxygen supply is never cut off, much less when it is restored in time. The comment you are replying to explained this in some detail and provided (abbreviated) references.

> [hemoglobin] touched by CO becomes essentially useless for the body since CO has a similarly high binding affinity to hemoglobin as oxygen. Recovering from that pretty much requires replacing the affected red blood cells.

This contains two major errors. First, CO binds much more strongly to hemoglobin than oxygen, about 240× as strongly; if it didn't, CO levels would have to be almost as high as oxygen levels to have an effect, but in fact 0.4% CO in the atmosphere is enough to kill you in half an hour. The second error, contradicting the first, is your claim that recovering from CO poisoning requires replacing the affected red blood cells. While CO binds to hemoglobin more strongly than oxygen, it isn't that strong; the carboxyhemoglobin thus produced can in fact release its CO and become functional hemoglobin again, with a half-life of about 5 hours. If replacing the affected red blood cells were required, it would be eliminated in about 30 days rather than about 5 hours. If, on the other hand, CO had a similarly high binding affinity to hemoglobin as oxygen, as you said it did, then it would be eliminated in about a minute rather than 5 hours.