As a follow up to what I wrote at the end of the last week, I would like to suggest the Ramban in this week's parsha that addresses Pharoh's loss of bechira works well l'shitaso of his answer in P' Lech Lecha as to why the Mitzrim were punished. The Rishonim ask how Hashem could harden Pharaoh heart, thereby removing his freedom to choose whether or not to free Bnei Yisrael, and still hold him accountable and punish him for his actions. The Rambam seems to suggest that at some point a person may be deprived of bechira as part of the punishment for an accumulation of sins and bad choices (more on that here). Ramban, however, offers a different answer: it's not that Pharaoh's bechira was taken away, but to the contrary, only by hardening his heart would Pharaoh truly have free choice. Any normal human being faced with the prospect of facing repeated pain and suffering or conceding would at some point give in. That's not an exercise of choice, but an exercise of submission, an abandonment of freedom. Hashem made Pharaoh impervious to the pain and suffering of the makos so that he would be free to choose of his own volition which path to follow.
The Ramban in Lech Lecha suggested that the Mitzrim were punished despite the fact that the enslavement of Bnei Yisrael was decreed by Hashem because their motivation was selfish and self-serving; the Mitzrim enslaved Bnei Yisrael because it fit their agenda, not because it was G-d's will. The "tikun" for the crime had to be obedience to G-d's will for it's own sake, lishma. If Pharaoh would have given in because he wanted to avoid further makos, it would not have undone the crime -- it would just be more of the same of following what suits his own agenda. Pharaoh therefore had to be given the freedom to choose to obey Hashem's command simply for it's own sake, not because of threats or fear of the makkos.