Why was it necessary for the Chinese gov't to put this poor man to jail?

Because they don't want to encourage all people who regard themselves as some kind of victims to go public to protest. That guy did not only "try to appeal". He organized dozens of parents to protest and got interviewed by media. Chinese government do not want people to be organized in a way not controlled by the government, and it does not like any protest (except anti-Japanese ones). That's the reason. It was necessary to their point of view.