It's a great quote by Mr Sagan but it isn't applicable to all things
Of course not. But it's certainly applicable to extraordinary claims.
particularly if the person positing the claims isn't asking for your belief in them. If they are merely opening up a discussion on the possibilities then it matters less.
Except that the people we usually get on this forum repeating extraordinary claims, aren't the sort who simply say "OK, what about this then? Let's sit down and examine it logically and systematically, to see if it's actually true". Sure, they often
start with a pretence of objectivity, but the moment you start to expose the holes in the "evidence" presented, they become increasingly irate and defensive.
And why? Because they are, in fact, believers. They are not looking for a discussion; they are looking for affirmation. Try as they might, they can't hide their commitment to the material they are posting. They will deny and resist - even when all denial and resistance is useless - any argument or evidence that runs contrary to their dogma.
Their last resort is as predictable as it is feeble: "Well, I don't necessarily
believe this... I just think it's worth watching/reading/thinking about". Which always makes me wonder "OK, so why did you defend it so vehemently and become so aggressive with the people who spent their time refuting it?" And of course, that's the giveaway.