I agree with your statement that there is a difference between morality and legality. But legality without morality is not oppression.
Legality is the state in which people have to do what is right because they would face a penalty otherwise (in order to combine everyone's personal freedom). Morality goes further than that because morality does not just look at people's actions but also at people's motivation, their thinking, etc. Legality can be enforced by a state, morality cannot because no one can actually make someone else think a certain way. (I can prevent them from saying what they think, but their inner convictions cannot be controlled by anyone.) There are of course actual states that try to regulate the morality of their citizens but such attempts are futile. That is why actual laws can never be based on morality.
That said, actual laws need to comply with legality and since morality demands the same things as legality (plus things regarding motivation etc.), laws that are in accordance with legality are also in accordance with morality (but do not cover all areas that morality does).
So that means legality and morality are two mostly independent systems and while I would rather live in a moral world, I have to (and can) deal with the fact that I live in a world with people who are not completely moral and since morality cannot be enforced, I have to settle for legality (which is enough most of the time because it guarantees my freedom).
I totally agree with you in respect to copyright being unjustifiably used against society, though.