Yes, Rhology, not exactly the same religions, but the same disease. Faith.
It's a matter of good fortune that most of today's Christians don't follow the examples of the Old Testament any more. But there are some gaining ground.
Just like the majority of Muslims don't fly planes into buildings.
It is people like yourselves, who consider faith a virtue, that allow extremists of all religions to operate.
As demonstrated quite a few times on this blog, notably here, atheists have quite a bit of faith as well. Maybe you should think about specifying what kind of faith. Jihadi faith? I'm with you! Christian faith? Only if you think that radically loving people and wanting the ultimate best for them is dangerous and sick.
You don't understand the OT's relationship to today. Here's a primer.
who consider faith a virtue, that allow extremists of all religions to operate.
I am only too happy to encourage extremists of the Christian faith to operate all they want, all they can. For their faith is for the building up of the world and people's spirits, both.
OTOH, I discourage extremism of the violent strain like Islam, and atheism. Extreme Islam is dangerous b/c it is violent in its exemplar, Mohammed, and in its commands. Extreme atheism is dangerous b/c in the end, nothing matters. At all. Thus the atheist's passions are free to run in whatever direction he feels that day. And we know that people are evil at their base, so those passions will run to evil, to hurt, to theft, to murder, to selfishness. So it's all about the CONTENT of that faith.
Here's hoping you meet more educated Christians in your lifetime than you have so far, and that you learn from them more than you so far have.