I'm going with Arthur's answer. To answer the question of why the same doesn't apply to Christianity, I dunno, maybe because Christianity is a lot more widespread than just one area of the globe. Maybe because criticism of Christianity is less popular/ not a cultural phenomenon, more of an individual-here-and-there thing. Maybe because the shortcomings of Christianity are less stark. Maybe because Christianity is older and more globally entrenched so it's taken more as an Earthly given.

Religion is so hopeless, people want to have it and at the same time want to push it down the throat of others too and at the same time pick their personal choice of it and stick to it for unconscious reasons so stubborn, that some even could get nailed at wooden beams and they still would cling to it.

Because they're idiots.

Sometimes it is...the people who criticize Islam and never criticize Christianity (which worships the same God and has many of the same problems as Islam) are telling on themselves - the body count through history is comparable

Because it can be, depending on the circumstances