It's too easy to say "Christians think this" or "Muslims think this," and even "practice this" or "believe this" isn't always accurate as there are always exceptions.  Even saying "in general, Christians believe" still isn't helpful.   But getting to specific examples tends to exclude the majority, so pointing to a specific event such as a Christianity inspired murder, or the Crusades, or Westboro Baptist Church, or Ted Haggard, or Pat Robertson, or Hitler, it doesn't really apply to enough people other than being an extreme example.   For example, "Christians are generally good" (broad generalization) but look at the Crusades (extreme example).  How do you avoid these in an argument?