All criticisms have some kind of point, e.g. they might highlight a need for something to be explained better. This is compatible with saying no one ever came up with a good argument (good in the context of modern knowledge) for the Earth being flat, or something. If someone thinks the Earth is flat, then this is quite a good criticism of something -- and I suspect that something is his own background knowledge. We could discus the matter. If he had some argument which addresses my round-earth views, i'd be interested. Or he might not know what they are. Shrug.