No, you choose a side when you choose a side. The fact that, conceivably, you could have an influence on an outcome does not mean you are picking a side. That oppressor you "should" have opposed is the one oppressing. Even if you side with the oppressed in secret, there usually is a cost in outwardly aiding them. To demand that someone pay a price is to assert that one's life is not one's own. To voluntarily offer one's life may be heroic, but to demand it is slavery.