Dr. Salam: “Islam was very strongly research-minded until about Year 1000 AD. Then there was a big battle between the Sufis and the theologians (established religious leaders). Theologians won that battle. They (theologians) put an embargo on independent thinking in the Islamic world. That started the decline of science in Islamic world. They killed off (Mansur) Al-Hallaj and many others. Islam has no theologians (established priesthood) but you still need a stamp of approval from the religious establishment. They control the population (people) by declaring all dissenters non-Muslim (excommunicate them). This is still going on”.

source https://www.youtube.com/watch?v=cXDehJzuXAg