There is currently no system that can provide perfect anonymity against a global adversary (someone who has wiretaps on all links and can possibly inject data a

There is currently no system that can provide perfect anonymity against a global adversary (someone who has wiretaps on all links and can possibly inject data as well), and it's not clear if it is technically feasible to build one. There is also no feasible way of mathematically proving that complex hardware or software does what is supposed to do, which means that you need to trust the authors, and isolation against bugs with security impact is required.