The dismissive statement "people have made similar claims before, therefore this claim isn't true" is one of my pet peeves. You see it a lot around issues like

The dismissive statement "people have made similar claims before, therefore this claim isn't true" is one of my pet peeves. You see it a lot around issues like this as a way to not engage with an argument. It's an obvious fallacy: it doesn't matter if something was said in the past, or whether or not it was true when said before. The only thing that matters is whether it is true in this case.