>The race of the yabamiko scum got wiped out because someone started explaining echo doesn't come from retarded looking dogs but from how the sound waves act.
That's belief, not fear. And yes, the outside world doesn't believe in youkai and magic.
But that is different from being inside Gensokyo and knowing for a fact that yamabiko exist while at the same time echoes don't come from them.
Finally, I am making a distinction between belief and fear here. I believe youkai in Gensokyo could continue to exist so long as humans have belief even if they don't fear them.
I'd say that a lack of ignorance about echoes might prevent new yamabiko from forming, but it won't make Kyouko vanish in a puff of logic so long as her existence is known.