> Injecting spider venom isn’t dangerous as long as you get the dosage right.

Venom actively damages your cells, CO just restricts oxygen access.

> If doing this makes it possible to perform better, people are going to push the edge of the amount that’s “safe“. Right up to the limit. Tip toeing over the limit.

Not necessarily. It’s not like EPO where more is better, the benefits likely cap out long before you reach a dangerous level of CO, so going to “the limit” isn’t something that’s likely to happen.

> It’s CO. there’s a reason the government is always telling people to make sure they have carbon monoxide detectors.

Yes because your boiler might leak an uncontrolled amount of CO and, because it’s odorless, you don’t know if you’re breathing too much before you pass out and, subsequently, die. That’s a different situation than being in a controlled environment where you can set the dosage quite easily.