Nothing wrong with saying “I don’t know”.
None.
When a man lies he murders some part of the world.
– Merlin (Excalibur, 1981)
If you know something to be false and try to pass it off as truth, that is lying. It doesn’t matter how you phrase it or try to hide behind symantics like “I’m just asking questions” or “it’s just a hypothetical”.
That being said, it does not mean that you cannot contribute to a conversations if you are not an authority on a subject. If you are not sure or cannot recall a credible source for your information you can preface your comment with something like “I never confirmed the validity of this, so I may be completely wrong, but…”.
Or just ask questions instead of trying to chime in. If you’re unfamiliar with a subject then you should be listening, not talking.
It is always better to admit when you don’t know something, than to make up bullshit. Always.
If you know it’s false, it’s called disinformation.
Let me rephrase that: Is it better to lie or say nothing at all?