The issue of proving open Kufr by a ruler in order to Islamically justify rebellion against him is extremely dangerous, but, frankly, in the current era of global corporate imperialism, it is largely irrelevant because our “rulers” are not our rulers; they are slaves to whom our rulers have delegated a certain degree of management duties.
If rebelling against the kuffar who actually dominate and control our societies must include fighting those institutions and individuals charged with enforcing and protecting the supremacy of the owners of capital, I do not see anything controversial about this in the Shari’ah.