Is "I Don't Know" ever a good answer?

Always. More people should do it instead of making up a shit answer.

Yep. There are questions whose answer we will probably never know. Besides, depending on factors such as relevance and time/resource constraints, sometimes a question may simply not be worth, or even practically possible, to explore.

There are many questions ive been asked that i didnt know the answer to.
So....yes.

Yes. Unless one knows (or can figure out) absolutely everything, there are bound to be times when that's the only honest answer.

I don't know. Is it?

Yes, a true statement is much better than a false answer.

It is when being interrogated by law enforcement officers.

Better then lying

If said honestly, yes.

Ever? Of course!