For one christianity doesnt say its okay to behead disbelievers, kill gays,
The bible on killing gays:
"If a man lies with a male as with a woman, both of them have committed an abomination; they shall surely be put to death; their blood is upon them." Leviticus Chapter 20 verse 13
The bible on killing unbelievers:
"If there be found among you, within any of thy gates which the LORD thy God giveth thee, man or woman, that hath wrought wickedness in the sight of the LORD thy God, in transgressing his covenant; 17:3 And hath gone and served other gods, and worshipped them, either the sun, or moon, or any of the host of heaven, which I have not commanded; 17:4 And it be told thee, and thou hast heard of it, and enquired diligently, and, behold, it be true, and the thing certain, that such abomination is wrought in Israel; 17:5 Then shalt thou bring forth that man or that woman, which have committed that wicked thing, unto thy gates, even that man or that woman, and shalt stone them with stones, till they die." Deuteronomy 17
Not beheading, I grant you. But stoning to death is hardly a more tolerant approach.
The bible is quite similar in this stuff to the Koran. The difference is how people read and enact it today. True, there are sects in the Middle East that take the Koran literally, and try to enact it. But plenty of small-scale sects also take a lot of the bible literally - that's why we call them findamentalists. And the Polish Catholic church takes it more literally than e.g. the Anglican or Dutch Protestant church, when it comes to things like gay people, women's rights etc.
It's not black and white, with Koran bad and bible good. Both are crazy, violent, poetic, scary, beatutiful books, written thousands of years ago. Today there is a sliding scale in how literally people take these books, from your British state (where head of state is defender of the faith yet gay marriage and abortion is allowed) to your Polish state which is supposed to have separation of church and state yet where neither gay marriage or abortion are allowed due to Catholic doctrine. You can see almost the full range within US states. And then there's the muslim origin states, ranging from easy-going ones like Turkey (until Erdogan) to your hardcore fundamentalists like Saudi.
So I don;t think you can claim one religion is more 'humane' than another. It's not the books that are the problem, it's the people. And there are plenty of intolerant people on both sides. I agree, the most intolerant state-sanctioned interpretations are in islamic countries, but let's not pretend that Christian countries are hunky dory edens of tolerance. I'm neither Catholic nor Muslim, and to be frank, as a native European, I am wary of both. You have to remember that North Europe's religious wars were Catholic vs Protestant long before the muslims turned up ;)