If you switch "allowed" and "banned", that would be Facebook, twitter, google, youtube, BB gun, etc. To your question, you underestimated how willingly Chinese government is to ban things. I think Islamism should be banned.
@Weimin there're long history and lot of cases Islamist do bad things without punishment, covered by the harmonic policy of government. And the majority Han group have concede a lot but they thought that was just reasonable and even want more. We can't stand it anymore.
@jay99 there're islamic autonomous regions like 宁夏. In year 2016, their financial income was 38billion RMB, but they spend 125billion. WTF! They build luxury mosques! We will be happy they go independent and starve themselves.