We don't have time to dissect everyone's arguments on merit and perform deep analysis. It helps sometimes to filter based on obvious criteria. Like if someone is a young earth creationist or believes the moon landing was faked. This belief so clearly denotes a lack of critical thinking that dissecting the rest of their arguments that follow is not worth the effort.

The world is so massively full of such low hanging fruit that you can often save a massive amount of time this way as it turns out the majority of people aren't worth listening to outside of narrow areas of knowledge they directly interact with. Its a completely valid strategy. The danger of course is that you risk ignoring useful proof if what you assumed was obvious was incorrect.