A hard fork provides a means to freeze The DAO and its children and return invested funds to those who hold tokens – without rolling back any unrelated transactions. The argument against a hard fork is that it undermines the essence of what a smart contract is meant to be: cold hard logic that can be guaranteed to execute without the interference of human hand.
For such reasons, execution of a hard fork to recover the funds is a bitter pill. However, there are the following compelling arguments for doing it:
Ethereum is less than a year old. Extraordinary actions taken now to protect the fledgling network from an extraordinary event do not set an eternal precedent.
Bitcoin itself hard forked (in August 2010 when it was significantly older than Ethereum) to address a protocol bug that allowed infinite bitcoins to be created. The hack of The DAO was not an Ethereum bug but such risky mass actions and code vulnerabilities will be far rarer in the future and this problem was equally related to the network being at a nascent stage of development.
A hard fork is really a protocol change. The protocol is nothing less than an expression of the ultimate consensus of the decentralized community. If the community wishes to adopt a protocol change in extremis to address a clear and present danger to its network, then this is arguably justified.
Source: Petition · Ethereum: Hard fork Ethereum to revert the hack of The DAO · Change.org