You can understand why Chinese authorities consider Liu Xiaobo such a political threat. His call for democratisation and peaceful political transition may sound moderate to people living outside China. But the demands to allow multiparty politics and a separation of powers in the "Charter 08" political manifesto he co-authored amounts to a direct challenge to China's one-party rule and its monopoly on all the key branches of government. You can call it what you like, but switching to having multiple parties competing for political power would effectively amount to a regime change from the current political system monopolised by the Communist Party.
The case against dissident Xu Zhiyong is more difficult to justify. The law lecturer is far less subversive; he is not challenging the central government's power or its legitimacy. He has merely called for what President Xi Jinping and former premier Wen Jiabao have themselves demanded. In one of his last major speeches before he left office, at a State Council executive meeting, Wen urged reform and repeated the call to uphold the rule of law.
Xi has made it one of his policy priorities to crack down on corruption and impose austerity on party cadres. Yet Xu has been jailed for four years, ostensibly for "assembling a crowd to disrupt public order". But no serious independent observer doubts he is being punished along with several others for being part of the New Citizen movement, which has campaigned to compel officials to disclose their assets.
Doesn't the movement's aim coincide with Xi's anti-corruption drive, which has extended far and wide, having had almost 37,000 officials investigated last year? Powerful officials have been targeted, including Zhou Yongkang , the former security tsar, and Li Dongsheng , a former deputy national police chief.
Both Xi and Xu are demanding cleaner government. But some official investigations into corruption also sound like purges as part of Xi's drive to consolidate power. For example, Zhou and Li were reportedly close associates.
Xu wants fair disclosure laws that would apply to all relevant officials, including some very rich state leaders. Xi's anti-corruption is far more selective.