Kerry, here is what Wikipaedia says about the controversies surrounding Gulen.

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Controversies

Gülen is a highly controversial figure in Turkey. Despite his large number of followers and significant influence in Turkish society and politics, he has been living in the US since 1998. While his followers and a significant part of Turkish society respects him as a humanistic figure at the service of Islam, a large fraction of society perceives him as a significant threat who aims to transform the country's secular system, allegedly by gaining followers in high places and brainwashing school children.[21]

In 1998 a scandal developed in which Gülen was claimed to have urged his followers in the judiciary and public service to "work patiently to take control of the state."[22] Several months before this scandal broke, Gülen had moved to the United States, to receive better treatment for his health problems (he suffers from diabetes and a range of its side effects) though some allege that this move was made to avoid his standing trial in person. In 2000 Gülen was prosecuted for inciting his followers to plot the overthrow of Turkey's secular government. He was acquitted in 2006.[23]

The authenticity of the tapes used in the scandal is debated. Gülen himself explained that the footage in question was completely taken out of context (he was giving advice to a group of official employees who felt marginalized by other groups within the state system that wanted them gone), and that he can't be judged for intents, only deeds.[24] Accordingly, he advised them that they should not relinquish their careers out of religious fervor but that they should remain in order to do good for the people, even if this meant not practicing their religion in the open. However, critics of Gülen argue, Gülen's own writings, some of which is quoted below, are in accordance with the ideas mentioned in the tapes; he pushes to make Islam the guiding principle in society while at the same time advising his followers caution and an embracing attitude until the conditions are ripe.[17]

Gülen's appeal to various ideological strands in Turkey differs. His supporters probably constitute the most influential Islamic and political movements in Turkey both for its human and financial capital. Various other shades of the Islamic movement and conservative segments of society are generally sympathetic to him. His detractors are mostly in the nationalistic wing of the secularists, critical of his alleged affinity for a theocratic society and his strategic support from the US. For the elites, the ranks are broken by certain liberals, who point out that Gülen's group, at least in its public representation, has proven to be most willing to evolve and most open to international influence.

Due to its spearheading westernization and secularization since the late Ottoman era, and later founding the secular republic under the leadership of Mustafa Kemal Atatürk, the military has always viewed Islamic movements with suspicion and since the 1980s has identified Gülen's group as a threat to the republic. In 1986, a military court revealed Gülen's supporters had infiltrated the military academy and the group was purged[18]. From then on, the Turkish military has repeatedly alleged that Gülen tries to infiltrate its ranks and pressured politicians to take action against Gülen.[25]
Gülen was widely criticized in 2004 when he, in contrast with his public calls for tolerance, commented that he considered terrorism to be equally despicable as atheism.[26] In a follow-up interview he declared he did not intent to equate atheists and murderers; rather, he wanted to highlight the fact that according Islam both were destined to suffer eternal punishment in hell.[19] Gülen does not deny the idea that there is Islamist terrorism,[27] that is, he agrees that such terrorism exists but argues that Islamist (a violent deviation from the true path) is not Islamic or Muslim, and has written an article in response to the September 11 attacks saying:[28][29]

We condemn in the strongest of terms the latest terrorist attack on the United States of America, and feel the pain of the American people at the bottom of our hearts.

Controversies over Gülen are even enhanced by his interfaith dialogue activities including meeting with the Pope John Paul II.