So they used a lot of suicide bombs against the crusaders? Dynamite was invented 150 years ago. I'm guessing that suicide bombing wasn't all that prevalent before that. Or what do you think?
Ever heard of the Assassins?
There's so much wrong with this. The DaVinci code or The Illimatus Trillogy are not works of historical fact. Both have admitted to taking things out of context and made up all manner of stuff. The historical assassins are Ismaili. Which means they have a new prophet after Muhammed and should really be considered a wholly new religion. They are very different. And are still often suffering from persecution from other Muslims because they are perceived as rejecting Mohammed.
Quite quickly after their rise, (the Fatamid empire) they came into conflict with the Caliphate on the ascent, the Seljuks. Weak and on the wane they turned to the only military option open to them, assassinations of opposing political leaders. But perhaps most importantly they're mostly mythic. The image that spread about them was the image created by the winners (not Ismailis). The whole idea of the Ismaili as ruthless assassins is mostly political propaganda. We also know that the version of the myth that made it to Europe came from Marco Polo, who is today primarily well known for just making shit up and exaggerating.
We have no idea whether the Ismaili assassins ever managed to kill anybody. And even if they did, we know from historical records they never managed to kill anybody of any note. All their prime targets lived to a ripe old age.
Also worth noting is that assassins were often used for political gains all the time everywhere. The middle east was not unique. They're certainly perceived a constant threat by rulers and often mentioned in ancient texts. Every European king had a food taster. But these are also times when people dropped dead from stupid little infections all the time. The knowledge of forensics and poisons was negligible. People were most likely murdered left and right. We have no idea how many of the deaths attributed to murder, was murder. And which murders went unnoticed. This is extremely murky territory.
But just the fact that you bring up an ancient myth does show us a couple of things.
1) You don't let reality, or what is reasonable, interfere with your firmly held beliefs.
2) Your grasp of history is not the best.
3) You don't look things up before posting.
Did I miss anything?
edit: fun detail is that the Muslims who conquered the Ismailis/Fatamids, the Seljuks were for practical purposes pagans. They kept all their pagan traditions. They just switched the names around a bit. They were pagan political opportunists who held a veneer of Islam to make ruling easier.
Another fun fact is that both the Fatamid and the Seljuk empires were extremely well run. Low corruption, good education system and a meritocratic system of exams if you wanted a job in the government. They were way ahead of Europe. These dynasties kicked off the so called Islamic golden age and is why there's so many mathematical and stellar terms that still have Arabic names today.