I agree that the US is different from most countries in terms of how difficult it is to prove slander and libel. But I don't think your description is quite accurate. Then again, I'm not a lawyer.

> The truth is a perfect defense. Even if you thought you were lying, you are protected. If you believe what you are saying, you are protected.

IIUC the truth is a perfect defense in most states, but in some states maliciously stated truths (insults, more or less) can be defamatory. For example, see Johnson v Johnson in Rhode Island, where one Clifford Johnson was required to pay compensatory damages for (more or less accurately) calling his ex-wife a "[redacted] whore" in public. (He was also initially ordered to pay punitive damages, but that was reversed on appeal.)

> If you did not know for certain that you said a lie, you are protected.

I don't think this is the case in most states. If you say something with reckless disregard for the truth, it can be defamatory.

> If you did not mean to cause harm, you are protected.

I think this is typically only true of defaming public figures.