I'm going to bed, but I want to make sure this gets out just in case other people decide to jump in on this conversation.
Koishi is almost invariably going to say things that will piss you off. Hell, she might have already done so. If that happens, shrug it off. Let her be a jerk. Be the better woman. And for the love of God, do not start insulting or questioning her core moral system. She has been holding onto her beliefs for a bloody long time and the strength of those beliefs shot up like crazy thanks to the Gensokyo Isle incident. She will not take kindly to having her view directly challenged, and she has already demonstrated that she has a short ragequit fuse. Don't tell her she's wrong, show her she's wrong.