Hizb ut-Tahrir just met in Chicago, and no one seemed to mind. But the Turkish authorities obviously view the group as a threat. Evidently if Sharia is going to come to Turkey, it is going to come from Erdogan and Gul, not from Hizb ut-Tahrir.
"Turkish police arrest 'Islamists,'" from the BBC, July 24 (thanks to Davida):
Turkish police have arrested almost 200 people suspected of being members of the banned Islamist group Hizb al-Tahrir al-Islami, reports say....Founded in 1953, Hizb al-Tahrir seeks to establish a pan-Islamic state covering all Muslim lands. It is banned in many countries throughout the world.
The group is widely viewed as extremist and anti-Semitic. However, it denies these charges and says it preaches non-violent political Islam.