And there is the problem. While you propose an interesting academic question, the chain of events starts from a law that I see as harmful. Therefore, there's no value in justifying the legitimacy of the next steps.
The suggestion that defamation should be generally legal is somewhat outside the norm, as far as I know.
If I start a campaign, billboards and all, saying that my doctor is a pedophile once convicted of rape in Australia who has been also implicated in organ trafficking (when she's actually very wonderful) then I should be held liable for the damage to her career and reputation, at a minimum.
I'm not a lawyer, but I think the USA has a reasonable position on how much defamation should be tolerated.
Slander and libel are illegal, but the threshold at which the law takes effect depends on how public the target is.
As such care has to be taken when making statements about a private citizen, e.g. "Mr. X is [something horrible]", but one can say almost anything about a public figure like the president, or senators, without fear of legal trouble.
The legal libel standard for public figures from NY Times v. Sullivan and Curtis Publishing Co. v. Butts is that you need to be able to prove "actual malice" (rather than something merely being untrue) which is of course hard to do because it speaks to intent.
Careful with that though, as we saw with the covington kids, if powerful interests want to slander AND libel you, they will drag you kicking and screaming into the spotlight. Now you are a public figure, now you are fair-game, but they've always seen you as fair-game, they just needed to manufacture justification.
That's absurd, though. It's pretty easy to determine when someone passes the threshold from private/unknown citizen to public figure. If the alleged slander/libel happened before that point, it shouldn't matter that they've since gained notoriety.
Based on your example, I guess that's not how it always works, but there's no reason in principle why the laws and legal standard around it could not be fixed to be more fair.
"Public figure" does not mean "elected official". It means literally anyone who publishes (makes something public) themselves. So anyone with a social media following is a public figure. If you have to worry about being defamed, then you are already outside the protection of defamation law.
There's also the concept of a "limited-purpose public figure", which means that just commenting on something can make you a public figure in certain contexts. For example, if you were to merely say that I was a pedophile, you probably have defamed a private individual. However, if you replied to this post with something like, "You probably just think defamation law is good because you're a pedophile that doesn't want to get caught"; defamation law could take your side. After all, I joined this particular controversy by commenting on it, that makes me a limited-purpose public figure. So even if you're not a public figure, it's very easy to accidentally become one.
I suppose it would not be such a bad thing to educate people to do their own research sometimes and not believe everything they are being fed. Were it the majority of cases, we would probably not be talking about this to begin with. What makes things worse is quantity of people making the same claim, or claims coming from authority figures.
What you're proposing here doesn't scale. What if everyone decided that there's no value in justifying the legitimacy of the next steps following the existence of laws they each saw has harmful? If everyone did that, there would be no laws left to enforce...
And there is the problem. While you propose an interesting academic question, the chain of events starts from a law that I see as harmful. Therefore, there's no value in justifying the legitimacy of the next steps.