Fallacious arguments (of which circular arguments are a subset) aren't literally meaningless. "My point is true because my point is true" is perfectly comprehensible, it just fails to establish the fact that "my point is true". You can disagree with it reasonably by pointing out the fallacy, so it has linguistic substance, and it is not meaningless.

It is very different from, say, "colorless green ideas sleep furiously" which is literally meaningless.