Anscombe's Antidote
According to Duncan Richter in his book, Anscombe's Moral Philosophy, her position on what is good behavior boils down to this: There are certain states of affairs to do with human beings (being a human) which are part of the nature of humankind. That is, they represent practices, institutions, ways of being in the world that are part of what it means to be human. Those acts that are morally good will be seen to express, reflect or be consistent with those human activities and institutions. Given her strong religiosity (she was a committed, practicing Catholic) she holds that these natural human propensities are part of God's plan for mankind and so consistent with what God wants for us. Therefore, to abide by them is to conform with God's will. But we do not do them because God commands it. Moral actions (or ethical behavior, since she rejects the notion of "moral" as inappropriate for our age -- a period in which we view the divine differently than mankind once viewed it) is thus to be consistent with God's will but not necessarily to act out of the desire to obey.
Anscombe thus rejects a morality based on duties. To have duties implies some kind of adverse repercussions for failing to obey them but moral claims (perhaps "ethical" claims better captures her view here) have no such consequences in and of themselves. That is why we can act immorally if we like, with impunity (other than some prospect of a judgment visited upon us in the afterlife which not everyone will grant even though everyone is presumed morally assessable in this life). Duties imply commands and an enforcer who punishes deviance from those commands. To suppose one has duties without the possibility that one can suffer adverse consequences for specifically failing to fulfill those duties is to render the very notion of duty empty. Richter doesn't maintain that Anscombe rejects the idea of duty per se though . . .