"And you shall remember that you were a slave in Egypt, but the Lord redeemed you from there, therefore I do command you on this mater." -- Deut. 25:18. (emphasis added)
The standard interpretation is that being a slave in Egypt should teach us compasion. But this is problematic in light of the fact that the verse uses the word "therefore" (Heb. "Al Kain"). If our experience in Egypt teaches us compasion, why does it not simply say "Because you were a slave in the land of Egypt?" Or even "that you shall remember that you were a slave..." Why must Hashem command us to obey not merely the dictates of justice, but to observe principles of social justice because we were slaves in Egypt?
I propose the following explanation. If we look at the world today, we do not see that those who have suffered (particularly those who have suffered unjustly as a people at the hands of another people) show empathy as a consequence. To the contrary, usually they use their suffering as an excuse to engage in selfish or mean conduct. "When I was weak and poor, others took advanatge of me. Why shouldn't I get my share now that I have power?" This is even worse if it is a matter of one people historically oppressing another. "Look," say the Shia of Iraq (for example). "You [the Sunni] oppressed us under Sadam Hussein, now we shall rise up and oppress you! Ha! See how you like it!" It does not matter that the average Sunni lived a pretty miserable existence under Sadam as well. It is enough that, of all the people under Sadam, individual Sunni did better than others, so therefore all Shia have a right to rise an "pay back" all Sunni.
I have used the most recent example in the papers. But whether it is sticking it to goyim for all the antisemetism in the world, sticking it to "the man" for keeping us (whoever we are) down, it is sadly human nature. A servant when he reigneth does not show compassion on account of his former sufferings.
God therefore commands us to obey the dictates of social justice because we were slaves in Egypt. He teaches us that the experience of slavery should teach us compassion, rather than allow us to excuse ourselves when we act unjustly against our fellow human being. Thus, God commands us "because" we remember our former slavery, and should remember that it was God who redeemed us so that we could live a life in accordance with the principles of social justice as expounded in His Torah.