I think a lot of people are missing the point when it comes to light side and dark side. There are a lot of sides to consider in the argument (pun intended).
There is what a council of Jedi think is light side. There is what an individual thinks is light side. There is what the Force itself thinks is light side. None of these things have to agree with one another.
Part of the reason the Sith keep rearing their ugly heads is because the Jedi don't have it all figured out. They only think they do.
An obvious example is the Jedi feelings about love. Like it or not Love for humans is intrinsically tied to reproduction. Force sensitivity is an inherited trait. If the Jedi don't get busy then each generation will have fewer force sensitive members. It takes too much effort to raise a child if you have nothing invested in them (i.e. love them).
To deny love makes Jedi stupid. Stupid is a form of unintentional evil and thus you could conclude that Jedi who deny love are dark side. Hence what the force thinks is different from what some Jedi Councils have erroneously concluded.
Things to think about in your game:
Is Obi-wan evil when he chops Darth Maul in twain?
Does it matter whether Obi-wan used a lightsaber, or tore Maul in two using the force? Dead is dead after all.
Is Luke using the Dark Side when he goes all righteous fury on the Storm Troopers after Obi-wan's passing?
Was it Anakin's love of Padme that lead to his fall or was it his obsession with thwarting death?
My thoughts:
To the more discerning person there is no light or dark side. Only outcomes and intentions. The Jedi rigidly control themselves because self-justification leads to corrupting one's own soul, not because a given action is inherently light or dark side.
A Jedi is evil when he kills out of vengeance or blood lust. He is good when he kills to protect, or end suffering.
Yes, Yoda is sometimes wrong. Gasp! Without anger there is no emotional counter to fear, which is why Jedi are so careful to feel nothing, but without feelings there is no life. Without life there is no Force. If the questions where easy we wouldn't need to tell stories to explore them.