You are right. Two wrongs don't make a right, yet that is the argument that was being implied. Christians have done bad things. And those conditions were corrected. Can you say the same thing about Islamics when they do bad things? Do other Islamics speak against, and even fight, other Islamics? Christians did.
Absolutely. The history of Islam has been almost as filled with intramural wars as the history of Christendom. It's just that they seldom speak against or fight each other for being too hard on unbelievers.