Why was Avner Wishnitzer thrown out of service in 2003?

Avner Wishnitzer, an Israeli veteran and liberal Zionist, believed the Israeli efforts in Gaza and the West Bank were nothing more than unjust occupation, and so refused orders to serve in those areas after learning of the attempts of some Israelis to run Palestinians off their land. Even when Palestinians launched terrorist attacks in Jerusalem and Tel Aviv in 2003, and even when this caused the loss of liberal support for Palestine, Avner stood his ground and refused to serve in territories he considered to be unjustly occupied. Avner even signed a public letter to his effect, and when he refused to withdraw his name, he was thrown out of the service.