An humble but just interjection About "True Youkai Extermination"...
Marisa is not an human villager,"she would be a "human eccentric" nor "magicians youkai" are normally dangerous to Gensokyo's balance and health...

...Be as it may the "True Extermination" would not be as "extermination lethal" as inflicted upon the ("Forbidden Scrollery")"Jinyou(*Youkai-turned human-dark arts)Fortune Teller,formely a suicide human reasearcher and studen about fortune-telling "because the greater effect, beyond sealing-grade("Forbidden Scrollery"->"(Sealing)Scroll of the One-Hundred...",(Sealed)Enenra","Sealed Evil Dragon",all the "Youkai-sealing Youma Books".)is "upon the more evil/wicked/maliciously impure"the being is such as was the *Jinyou Fortune Teller,who is an evil spirit-born Youkai,strongly hinting to be equal to a fully-malicious evil spirit ,youkai like the ..

...The "opposite example" is upon the ("Forbidden Scrollery""Young(Youkai)Fox Student" which was shown to be harmless and pliable to pass through it , the "Hakurei Trap-Panel imbued with the "Hakurei God and Hakurei Shrined virtue of extermating Youkai" ,because "as innocent as possible".