Opinions I guess. For me, it shows some sort of effort. Enough care to actually attempt to support themselves and make an actual argument. It doesn’t mean they are right, never said it did. It is about the art of crafting a well-formed argument. If the only thing you can do is attack their source, you have forfeited the argument because it is a bad-faith retort. He says that it hasn’t happened, then provides what he considers to be a credible enough source. You want to retort him, find a source that is at least equally credible, and provide it. It is discourse and proper form. Everyone needs to learn a bit about it and become better citizens to each other. Maybe if we did we could avoid so many messes.