It's always useful to think of these situation in circumstances where you don't have any emotional involvement because otherwise you mind can play tricks on you.

For example imagine you are a European Scientist who really wants to fit every animal onto tree structure with mammals over here and squid here and all the animals fall into some easy to understand structure that makes total sense to you.

And some weird guy comes back from Australia with natures most awesome animal the platypus. A furry creature that lays eggs with poison feet. Your simple identification chart is totally jacked. It way easier to say he is a quack that evaluate the evidence you don't like. Heck it's totally inconvenient that your life's work is wrong, it's going to cost you money and esteem.

tldr; pointing out a quack is a great excuse for avoiding evaluating their arguments but refutes none of them. Everyone's time is valueable and figuring out what adventures to spend it on is important. Confusing that reasonable justification of where to spend your time with their argument being false is a dangerous habit to get into. You end up always thinking you are right and avoiding things that challenge your beliefs.