I don't agree that doing nothing can be Evil. I agree that not helping can make you Neutral, but it can't make you Evil. Walking away from a situation should always be a valid Neutral option.

I think it's also important to remember that a lot of cosmologies will consign Evil souls to one of the Lower planes upon your death. It would be really, really weird to be sentenced to an eternity of torture just for thinking Evil thoughts, and I am pretty sure the 3.5 alignment books outline that you must do something Evil to be Evil.