It is important to chalange the spread of misinformation even when you don't have time to prove the correct information. If that statement was left unchallenged it would be seen as a tacit endorsment. The amount of effort you have to invest is proving that breakfast dosn't ward off tigers is disproportionate to the benefit.
that makes sense if other people are watching the conversation, paying attention to it, considering everything that's said and using that as the basis for what they believe going forward, but that almost never happens, and certainly never happens here.