The assumption that someone who can’t communicate pain is unable to feel pain seems misguided at best.
All of a sudden the decades of research that had been interpreted as showing babies didn't feel pain was overturned and new research showed they did.
Medical research really is mostly a series of fads.
What would you chose?
I'm not saying that this is the exact case with infants. Just trying to illustrate there might be valid reasons to inflict temporary pain to save health.
Anesthesia usually includes drugs with distinct, separate actions, like an analgesic (to block pain receptors), muscle relaxants (so patients can be moved/organs accessed), CNS depressants (to prevent unexpected spasms disturbing the surgeon), coma-inductors (so patients don’t chat with the staff and freak them out after practicing on cadavers for years), and amnesia-inductors (because surgery is kind of gross).
We know enough about them to use them safely, but most anaesthetic drugs are somewhere on the spectrum from "not fully understood" to "a complete mystery". Science knows how anaesthesia works in the same sense that I know how a car works - I can push the pedals and turn the wheels with sufficient proficiency to get to the grocery store in one piece, but I'll be damned if I can explain what's happening under the hood.
> medical science isn’t so good at explaining why the drugs have these actions
you can see I'm in full agreement
On the other hand, painful stimuli tend to (e.g.) increase a person's heart rate and blood pressure, and that the proper anesthetic plane blocks those responses, so it's clearly doing something in the moment. What we don't know every well is the mechanism of action for general anesthetics.
It's not just "it's hard and we're lazy so lets make up an excuse" like you seem to be implying.
Edit: Since apparently it wasn't clear, we're talking about the timeline when this issue was hashed out, so the 1980s. Anesthesia carried substantially more risk then because back then we didn't understand it nearly as well.
It's one thing to say, we're not going to use anesthesia because it's too much risk, it's another to say that they don't feel pain at all so let's not worry about it.