It is important to distinguish that Ethereum is not responsible for what happens to Ethereum classic and also in the DAO because the DAO was operated completely independently of Ethereum. However, a $ 50 million hack has dissolved public confidence in Ethereum,.
Ultimately, the decision to fork is based on the fact that 50 million ethers remain in the child DAO of the hacker and can not be reached for 28 days due to the DAO Smart contract
Ethereum classic kept the original idea of ethereum while ethereum improvised on it's ideology.