So personally I'm not so sure how 'fragile' their fragile power is. We also don't know who may already control that power.
Yeah, ghash.io is a concern. One problem is that we lack any kind of organised form of communication for miners. There's the miner subforum here but I bet a lot of people don't check it, and the p2p alert message but a lot of miners don't run a full node. We need a carefully controlled (so it's not noisy) miner announcement system.