The truth is generally not up for interpretation by any person who feels it should be. Critical thinking is actually a thing, and the lack of it does actually result in believing false things. If someone told me that I'm not applying critical thinking, then my response would be to ask for specific details on what aspect of critical thinking I'm not applying and exactly where I'm getting things wrong. What I would not do is respond by criticizing the idea of critical thinking itself or tell them that they need to consider alternative facts.

500 years from now I have absolutely no doubt that there are things we absolutely believe to be truth to be proven wrong. (Maybe light isn't both a wave and a particle?)

Heck, maybe antibiotics do contribute to autism some how. I very much doubt it. But it would be hubris to assume I know absolutely everything there is to know about the human body, antibiotics, and all their interactions. So I disagree with anti-vaxxers, based on current evidence. But I won't dismiss them and consider them less intelligent.

We knew this 500 years ago too, but even if we didn't it would not have been rational to pretend to know the shape of our entire world without having evidence to back it up. All we would know is that it appears to be flat from our limited vantage point, and we were free to investigate further using various methods.

500 years from now I have absolutely no doubt that there are things we absolutely believe to be truth to be proven wrong. (Maybe light isn't both a wave and a particle?)

500 years from now it will still be the case that light can behave like a particle and a wave depending on how you're measuring it. We may have better, more accurate models to explain the behavior of light in 500 years.

So I disagree with anti-vaxxers, based on current evidence. But I won't dismiss them and consider them less intelligent.

The reason that many people believe vaccines cause autism is because of a fraudulent study by Andrew Wakefield. Believing in a claim based an a proven fraud is not rational regardless of what is discovered in the future.

To put it generally, if you believe in claim X for bad reasons, and it later is discovered that X is true, it does not mean that you were retroactively acting rational for previously believing in claim X for bad reasons.

That is true. Isn't it equally as true that if one goes around telling people they are wrong, and then it turns out that one is wrong (based on new evidence), one has been wrong AND a hypocrite? The temptation is to say "ahh, but THIS TIME we have better science!". That's always been the case.

My point isn't about truth and error as much as hubris, humility, and respect.

There is a difference between saying that a belief in a claim is not rationally justified and saying that a claim is false. Both sides of these debates can make mistakes. Those against believing in the claim can make the counterclaim that it is false, and they might not actually have justification for that. On the other hand, often those that believe in the claim misinterpret the other side as making the counterclaim when they are in fact not doing so.

In the case of autism there has been extensive research since the moral panic began, and no evidence for a link has been found where it was expected to be found, thereby bringing increased justification for the counterclaim. I think this is also true with many other unsupported claims out there that are popular enough to have been exposed to systematic scrutiny.