There are many great uses for pure oxygen. Just one example is for traumatic brain injury.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0079995HBOT therapy has many benefits.
Another study on breathing pure oxygen:
https://clinicaltrials.gov/ct2/show/NCT03268590Keep in mind that one observation and theory doesn't necessarily prove anything. If you think too narrow minded, you'll not only miss out on important information, but you will also mislead people.
It's not my concern if you miss out on anything, but I won't let misinformation stand on the forum. Misinformation being something that can be proven to be wrong. Or even something that is true but is shared in a misleading manner.
Like almost everything (including oxidation and anti-oxidation), both "opposites" in any system are extremely important, and understanding both (in this case CO2 and Oxygen) can be extremely beneficial.
People who take one side only, usually only have part of the picture. Like I said, this goes for almost everything: Hot and cold therapy, ions vs. particles, proton donors vs electron doners... The list is extensive.
Sometimes, the effect that we're looking for is a hormesis effect. You're doing something to challenge the body to correct. As such, many things are catalysts. Their direct action might be perceived as "negative", but when viewing the whole picture, the end result is therapeutic. Garlic is a good example. So is ozone.
Also, soda springs are not better than hot springs. They are just different.
Artesian hot springs often omit extremely unique scalar-wave forms, and the natural infrared energy is great for both stress and pain.
I'm sure that there are ways to take a CO2 bath (it is a simple gas), but it is very hard to replicate a good hot spring water taken in nature. I know, I've tried for decades.