There are obvious differences between Christianity and Islam that make Christianity able to coexist with a modern secular state while Islam is showing all over the world that it can't.
This is only because Christianity has changed. Christianity as it was during the era of the crusades, and for hundreds of years after them, not only could not coexist with a secular government, it couldn't even coexist with an ostensibly Christian government which espoused a slightly different form of Christianity.
Note that I'm not bashing Christianity here... I am a Christian. But let's not whitewash the history of Christianity.
can you imagine the Pope leading a frenzied crowd in the St. Peters square in chants of "death to infidels"
Well, historically, the Pope doesn't lead chants. Instead he just issues orders to root out and forcibly "convert" infidels via torture, to save their souls. Of course, popes haven't done that for centuries because it has become unacceptable to Christians.