I don't even want to know what their logic is for always voting "not guilty." I'm sure it will just anger me further.
I'm going to tell you anyway - the logic is that the entire system is corrupt, from the police gathering evidence to the judge that permits in the room to the law itself that prevents the accused from putting on an effective defense. Because you cannot trust the system itself to present accurate evidence and argue it fairly, the only way to assure that an innocent person does not go to jail is to vote "not guilty" every time.
In fact, I agree that if his premises are true, his conclusion does follow. If the entire justice system is geared toward putting the accused in jail regardless of actual innocence, then voting "not guilty" every time is probably the right thing to do.

