Rider calls herself evil, talks the part, yet she doesn't do anything terribly evil. It seems strange... Then you have to remember one thing: she is a pirate. As in the murderous thieves that earned the name of "Enemies of the Human Race", and comes from the era where pirates earned that name. Of course she calls herself evil: to people of her time (especially Spaniards) she is the ultimate evil (even if she was a corsair acting on Elizabeth I's order), she's just being Genre Savvy about it.
The game features a Saber who looks a lot like Arturia. The true identity of both Sabers were individuals who had legends that involved them returning from the dead.
Fox!Caster's Matrix is a bit of a Guide Dang It the first time around, however unlocking it can be chalked up to one question she asks about genocide in the fourth week. The best answer is to note that it is an always punishable act; if you call it unforgivable then, as someone who killed 80,000 people as the Stone of Nasu, she will understandably not want to talk about it.
The bonus boss, Shiki Ryougi, could have easily broken out of the Moon Cell at any time by killing it and very likely taking everyone inside with it. Why did she decide to fight 100 Servants instead? Because, for her, the only time she feels alive is in a fight to the death. She was taking that option for fun!
CCC has one that's a case of a accidental Fridge Brilliance. Yes Karna's Noble Phantasm risks oneshotting Caster is a gameplay result as she is a case of being a Glass Cannon. However, there is another and perhaps accidental reason:Karna's noble phantasm is a Anti-God noble phantasm. What is Caster's identity? Tamamo-no-Mae, A GODDESS!