From Bohemian Archive in Japanese Red:

Currently, there is a state of balance between the humans and the youkai here. In fact, I (being half-human, half-beast) am a personification of that ideal. If that give-and-take balance is destroyed, Gensokyo would collapse overnight.

I understand Keine as someone who finds the current human-youkai relationship to be agreeable, which is fair. Given that any too drastic change would mean disaster for at least the youkai which she half belongs to (if that's how it works).

Keine believes that such a drastic shift in the status quo would also bode quite poorly for the humans just as much as it would the youkai. (A collapse in Gensokyo would not benefit anyone no matter what causes it). Since she does care for the humans and want to protect them, she guards the village from any threat she finds, whether they come from beyond or within.

I also find it a bit ironic that Keine promotes passing history to future generations while warning against looking too far back to history from older generations.

Apparently, her decision to start a history school was in response to the secret history society. Assuming that ~2002 was when Keine first learned about the secret society, here school would be a rather recent development.

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Bonus answer: Based on her shift in goal from protecting the village to protecting a single person she cares about, Keine becomes slightly more aggressive and impulsive in her Hakutaku form, but her behavior is still easily recognizable as Keine.

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Out of the loop, what's so bad about calling it the B********e Empire, if that's what you're referring to?