The factor lying at the root of everything is that China's government is fundamentally illegitimate from the West's point of view. Because of this perceived illegitimacy, when a violent bombing/stabbing incident happens, the default assumption (so the West insists) to make is that it's an case of oppressed subjects fighting for freedom; the burden of proof is on the Chinese government to show that it's a genuine act of terrorism. Likewise when activity purporting to be terrorism prevention measures take place, the default assumption to make is that it's an attempt at ethnic cleansing ala Nazi Germany, the burden of proof is on the China government to show otherwise. At bottom it's a disagreement over where the burden of proof is located. Because both sides are operating with different standards of evidence it's a dispute that's basically impossible to resolve.