What is the fallacy fallacy (argument from fallacy)?

Concluding that because an argument FOR a claim is fallacious, the claim itself must be false.

The pattern: someone defends X with a bad argument; you point out the flaw; you then conclude X is false. It fails because a poor argument for a claim doesn't disprove the claim — only that this particular defence fails. The claim could still be true for other reasons.

A: "Eating vegetables is healthy because my favourite celebrity says so." B: "That's just an appeal to authority — so eating vegetables clearly isn't healthy."

A's reasoning is genuinely fallacious, but vegetables don't become unhealthy as a result. Spotting a fallacy lets you reject the argument, not the conclusion — to reject the conclusion you need a separate reason against it.

Tip: "Your argument is bad, therefore you're wrong" is itself the error. Refuting an argument and refuting a claim are two different jobs.