The entire point of the spell card rules is to be non-lethal, so that both humans and youkai can survive. Gensokyo, after all, was created to be a place where youkai would live on, rejecting the disbelief of the outside world. But to do so, they need people to believe in them and their power. Thus, incidents, and spell card rules.
Akyuu, though knowledgeable about youkai and the way Gensokyo works, is not a combatant. In fact, her writing of Gensokyo Chronicle and related works is part of an established balance, to keep the regular humans in line, and keep belief in youkai strong. Whether it is a deliberate scheme, or just a result of her personal belief, her statement serves the purpose of Gensokyo. The antagonism between human and youkai is literally what youkai need to exist, as long as the humans do not get too strong, or the youkai do not do something really stupid. But that's what Keine is for...on both ends.