That's your opinion on how people should speak, not most people's, so feel free to disclaim when you yourself talk, but don't deem what other people should or should not say.

I’m afraid you didn’t understand what I just said. I was politely trying to say “if you wisely abstain from talking about things you don’t know about, you won’t need to disclaim that you don’t know what you’re talking about.”

Or I can just say whatever I want, as can anyone. You can only contain your own words, if you would like to "wisely abstain," then do so.