As far as I understand, Xiaobao drafted a roadmap plan for China to go down a western democratic route and promoted it among an academic group. This would be a multi-party route free to argue in public.
What upset the Party was that it was made clear that China could not transform itself via this route, and that China has chosen to implement a 1-party internal democracy. This does not however mean that it will be like this forever.
Xiaobao's sin was to promote an alternative which was clearly rejected. For this, the sentence was 11 years in prison.
I do believe in the assessment that China cannot go directly into a multi-party openly debating democracy. It would be very disrupting as well as introduce tremendous uncertainty immediately. Which was why a 11 year sentence was imposed to deter the development in this direction.
It makes sense to me.
(I do not know whether my facts are correct, but that is what it appears to me).
Mandela is undoubtedly a hero. It was through his character and wisdom that he was able to attract the right people to support him, and to transition an apartheid into a democracy as peacefully as it had.