And it doesn't just happen in this book. I've read another book where the MC's love interest turns out to be the son of the woman trying to kill her. Or in another book, where it turns out that the MC's love interest was strongly connected to her brother's death, or in another book where the guy was a thief, etc. So, why is it? Why do us readers drink up all these stories about bad people who... actually aren't bad people? Why don't we hate them when we realize all they've done?
It's because we like to see a boy who's raised by people to think a certain way, to do certain things, and yet somehow rises above it a is a good guy. And even if he hasn't risen above it completely, then the beautiful wholesome girl comes along and his love for her convinces him to have a change of heart! Even better!
So why is it that we love to hear about redemption and all that other stuff I've already explained? It's because these people are showing us that we AREN'T a product of our environment, that just because were born in the slums doesn't mean we have to act like a slum ( or in this case, just because your raised by evil terrorists doesn't mean you are one), etc. And even if we don't consciously think/ feel it, when we see or read these stories of the bad guy turned good, we have hope that we also don't have to be a product of our environment. If they can do it, so can we( but our's would probably be alot less dramatic).
Plus, you know, there's just the fact that bad boys are hot. And everyone likes to read about that( ...well, at least girls do)