Earlier quoted context omitted.
I'm not sure what you mean. I've been under general anesthesia a few times and not had any negative consequences. My dad has had multiple brain surgeries, and he's fully functional. Most people I know have been under at least once. I think before you blame anaesthesia it's worth wondering what else happened to you on the table, or whether something else might be causing you the problems. A lot of other things happen…
Well, there's a small chance anesthesia can affect you negatively. Like all medical interventions, it can have side effects.
So we've departed from the realm of clinical analysis and entered the realm of hearsay and feelings. And on that level, such a claim cannot be challenged with facts or statistics. But what an irrational claim can be challenged with is equal assertions of irrational feelings toward the opposite.
In other words, I would challenge a rational claim with another rational claim, but I won't bother with that for people whose arguments aren't based on reason. In that case, it's best to throw out a hearsay claim in exchange for a hearsay claim, and save your facts for people who care.
The goal of winning an argument isn't to convince someone that they're wrong (if this person is even real or believes what they say), it's to show the flaws in their reasoning to whoever they're trying to convince.