These open resolvers are largely run by ISPs and resolve addresses for their customers. Taking them down would cripple the Internet access of their peers.
They do not need to be taken down; they need to be reconfigured. An open DNS resolver is (arguably) misconfigured, not malicious.
By being made public they can be used maliciously by third parties. If such ISPs are slow to respond and reconfigure, they are a liability to the whole internet and the fault is theirs. A suggestion such as GPs, while probably illegal, sounds like an interesting way to hasten them a bit. Better to have their customers on their heels urging them to get a grip, than the whole internet in jeopardy.
They do not need to be taken down; they need to be reconfigured. An open DNS resolver is (arguably) misconfigured, not malicious.