I would contend that the cases of real oppression were not caused by real Christians, or that the cases with real Christians were not cases of real oppression.
I recognize that this sounds like a "no true Scotsman" argument, but give me a moment to make a clarification. No True Scotsman arguments are made by adding to a definition, whereas Christianity is has authentication built into it ("you will know a tree by its fruit")
Oppression of any kind, especially in cases where persuasion could present a simple alternative, is a great tragedy. That said, the difference between oppression from so-called "Christians" and oppression from Islam is that "Christians" act in contradiction to the ideology they claim, while Islam is by-nature an ideology of violence (that said, most self-proclaimed Muslims are usually unaware of the violent nature of Islam, or are living in contradiction to their religion, and as such are very nice people)